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"NEW-WORLD SCIENCE SERIES 


HUMAN 

PHYSIOLOGY 


AN ELEMENTARY TEXT-BOOK WITH SPECIAL 
EMPHASIS ON HYGIENE AND 
SANITATION 


JOHN W. RITCHIE 

»\ 

PROFESSOR OF BIOLOGY, COLLEGE OF WILLIAM 
AND MARY, VIRGINIA 


Illustrated by 

MARY H . WELLMAN 



> -> > 

YONKERS-ON-HUDSON, NEW YORK 

WORLD BOOK COMPANY 



t w? ^ 


/?// 


NEW-WORLD SCIENCE SERIES 


“ Ow/* national health is physically our greatest 
asset. To prevent any possible deterioration of 
the American stock should be a national am¬ 
bition .”— Theodore Roosevelt. 

The conservation of individual and national 
health is the purpose of the Rilchie-Caldivell 
series. 

Primer of Hygiene 

By John W. Ritchie of the College of William and Mary in Vir¬ 
ginia and J. S. Caldwell of Peabody College for Teachers in 
Tennessee. Illustrated. Cloth. List price for class use 40 cents; 
mailing price for single copies 48 cents. 

The purpose of this first book is to teach the lower grade pupil 
what he himself can do to keep his body in health — personal 
hygiene. 

Primer of Sanitation 

By John W. Ritchie. Illustrated. Cloth. List price 50 cents; 
mailing price 60 cents. 

The second book in the series and the first in the English language 
to teach grammar grade pupils how to escape germ diseases and 
how to cooperate in conserving community health — public hygiene. 

Human Physiology 

By John W. Ritchie. Illustrated in black and in colors. Cloth. 
List price 80 cents; mailing price 96 cents. 

A third book which presents to upper grammar grade pupils those 
essentials of physiology, hygiene, and sanitation that every Ameri¬ 
can citizen ought to know. The style is so simple and the illustra¬ 
tions so clear that the subject assumes unusual interest. 

A fable entitled Tli° Adventures of the Starch 
Family , an aid to the understanding of the 
process of digestion , will be sent free to users of 
Human Physiology. 


WORLD BOOK COMPANY 

». € C. 

Caspar W. Hodgcon, Manager 
Yonkers-on-Hudson, New York 


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Copyright , iqo8, by World Book Company. Entered at Stationers’ Hall, Lo7idon. 

All rights reserved. 











PREFACE 


From a considerable experience with both very elementary 
and more advanced classes, the author has been led to certain con¬ 
clusions in regard to the teaching of elementary physiology and 
hygiene. It is not proposed to enter here into a discussion of 
the correctness of these conclusions, but a brief statement of a 
few principles that seem fundamental may perhaps be allowable. 

The chief object of teaching physiology in the public schools 
is to train the pupils to keep their bodies in health. The mere 
teaching of anatomy and physiology will not accomplish this, for 
the pupil cannot master the structure and workings of the body 
in a way that will enable him to frame the laws of health and 
apply them. Neither can the desired end be reached by teach¬ 
ing rules of health without an anatomical and physiological 
basis; for without such a basis, hygiene is an intangible and an 
elusive subject. The author has therefore concluded that a 
conservative middle course is wiser than either of the extremes 
of method mentioned above. An elementary text in physiology 
should be a balanced text, containing sufficient anatomy to make 
clear the broader outlines of the structure of the human body, 
enough physiology to make plain the great laws according to 
which the body lives, and a full discussion of how a violation of 
these laws may jpe avoided. 

For the introduction of certain new matter, as, for example, 
the cell idea, the work of enzymes, and matter relating to germ 
diseases, there is little need for explanation. The groundwork 
of physiology and pathology has in recent years so shifted and 
extended itself, that the subject-matter of an elementary course 
must to a considerable extent be altered if it is to furnish a 

iii 


IV 


PREFACE 


proper basis for hygiene. The importance of teaching the 
known facts in regard to parasitic diseases and of training 
American citizens to apply measures for the prevention of these 
diseases, is now recognized, and the reason for the .rather full 
treatment of communicable diseases will be understood. 

One other point in connection with the teaching of physiology 
has constantly obtruded itself upon the writer. This is the age 
of science, but instead of teaching elementary science in our 
public schools, we are teaching unrelated fragments from differ¬ 
ent parts of the field of science. Physiology more than any 
other subject is the people’s science, and it should be related to 
the nature study and the agriculture of the public school course. 
In a few places in this book an attempt has been made to lead 
the pupil into some of the byways that connect his physiology 
and nature study, and special emphasis has been given to cer¬ 
tain facts that are necessary to an understanding not only of 
physiology, but of other subjects in the public school curriculum. 

For counsel and very great assistance during the preparation 
of this text, the author must thank his friend, Professor J. S. 
Caldwell of Peabody College for Teachers. He is also under 
obligation to Mr. J. C. Freeman, who made the calculations for 
the table on pages 350-351; and for many suggestions and cor¬ 
rections he is indebted to the following persons: Dr. William H. 
Park, Research Laboratory of New York City; Dr. F. H. Pike, 
University of Chicago; Dr. O. P. Jenkins, Stanford Univer¬ 
sity ; Dr. C. M. Hazen, Medical College of Virginia; Dr. E. G. 
Williams, Virginia State Board of Health; Dr. S. O. Mast, 
Johns Hopkins University; Dr. J. A. C. Chandler, Virginia 
Journal of Education; Professor C. W. Hetherington, Univer¬ 
sity of Missouri; Miss Virginia Jones, Williamsburg, Virginia, 
Public Schools; Edward Hughes, Stockton, California, Public 
Schools; and W. I. Chapman, Natick, Massachusetts, Public 
Schools. 


CONTENTS 


TAGE 

Introductory . i 

CHAPTER 

I. The Human Body a Colony of Cells ... 3 

II. The Plan of the Human Body.16 

III. The Ruler of the Body.23 

IV. The Skeleton.31 

V. The Skeleton (< continued ).45 

VI. The Muscles.59 

VII. Foods and Energy.78 

VIII. The Digestive Organs.88 

IX. Digestion, Absorption, and Oxidation of Foods . no 

X. Dietetics.120 

XI. The Circulatory System.135 

XII. Respiration.160 

XIII. Ventilation.178 

XIV. The Kidneys and the Body Wastes . . . .186 

XV. The Skin and the Body Heat.191 

XVI. The Nervous System.210 

XVII. The Nervous System ( continued } .225 

XVIII. The Effects of Alcohol on the Human Body . 238 


V 












vi CONTENTS 

CHAPTER PAGE 

XIX. The Special Senses. 245 

XX. The Special Senses ( continued ).259 

XXI. Accidents .. 274 

XXII. Disease Germs. . . 285 

XXIII. Diseases caused by Protozoa. 292 

XXIV. Diseases caused by Bacteria. 303 

XXV. Preventing the Spread of Disease Germs . . 320 

XXVI. Tuberculosis. 340 

Appendix. 347 

Glossary.355 

Index. 357 









INTRODUCTORY 


Did you ever get up in the morning and find that all the 
world seemed bright ? And did you ever get up on another 
morning and find that all the world was dull ? Do you 
remember how on the one morning you sang over your work 
and ran on your way to school ? And how on the other 
morning you blundered and fretted over your work and did 
not care to play ? On the one day you were so happy that 
every one was pleased to see you. On the other day you 
were not a pleasant companion for any one. On the one 
day the world seemed a beautiful place, and work was easy. 
On the other day all the world was dull, and every task was 
hard and disagreeable. 

Why were you happy and joyous one morning and misera¬ 
ble and unhappy the next ? Why did you cheerfully do your 
work one day and hate the same work the next day ? Was 
it money, clothes, or education that made you happy ? Was 
it a lack of them that made you unhappy ? All these things 
are important, but there is something else much more im¬ 
portant than all of them, — something that causes happiness to 
bubble up within you no matter what the world is like; some¬ 
thing that keeps the heart beating strong with hope, and 
makes you laugh at hard work ; something without which all 
the wealth of the world cannot make you happy, and with 
which any sQund-minded person can lead a useful and a 


2 


INTRODUCTORY 


successful life. This something that can so change all the 
world for you is the health of your own body. 

We cannot always be in perfect health. Sickness is bound 
to come to us all, for there are many things about the human 
body that we do not understand, and it has many ailments 
that we cannot escape or cure. It is possible, however, for 
us to learn many things that will help us to avoid the ill- 
health that is so common in the world. In this book we 
shall, therefore, study the human body and how to keep it in 
health. 


CHAPTER I 


THE HUMAN BODY A COLONY OF CELLS 

When you view a brick house from a distance you do not 
see the bricks of which the house is built; but if you look at 
the house through a telescope or come close to it, you see 
clearly the bricks in the walls of the house. The house which 
from a distance appears to be one object is seen to be com- 



FlG. i. Cells. A is a single cell as it appears under the microscope; B is a cell 
showing that it has length, breadth, and thickness; and C is a group of cells. A cell 
found alone usually has a somewhat spherical shape, as shown in A. When cells grow 
in groups they press against each other and usually have an irregular shape, as shown 
in C. 

posed of a great number of smaller objects built together to 
form one whole. 

The human body is composed of many small parts called 
cells. When we look at the body we cannot see the cells; 
but when a small portion of flesh or skin or other part of the 
body is examined under the microscope, the little parts which 

3 


4 


HUMAN PHYSIOLOGY 


make up the body can be distinctly seen. As the walls of the 
house are built of bricks, so the human body is built of cells. 

The Cell. A cell is a small portion of a transparent, 
jelly-like material called protoplasm} Usually a cell has a 
thin wall about it, so that it is like a little sac filled with a 
clear, half-liquid substance. In each cell is a nucleus , which 
is a denser portion of the protoplasm. Both the nucleus 
and the less dense material 2 around it take in food and 
grow ; both of them are alive. Taken together they are the 
protoplasm, the living substance of the cell. 

Living Things composed of Cells. As a heap of sand is 
composed of small grains, so are living things composed of 
very tiny cells. 3 Every blade of grass,' every weed, every 
flower, and every tree is made of cells. Every animal, 
whether it be large or small, whether it live in the water, on 
the land, or in the air, is composed of cells. Dead materials, 
like earth, stones, water, and air, are not made of cells, but 
there is nothing living that is not composed of cells. 

How Cells are formed. The ancient Egyptians thought 
that crocodiles and frogs came from the mud of the river 
Nile, and a great Grecian philosopher believed that insects 
sprang from the dew. A wise old German once told the 
people how mice could be created from wheat and stagnant 
water. Two hundred years ago, it was commonly believed 
that maggots came from meat and cheese, and that worms, 
insects, snails, and eels came out of decaying matter and 

1 In the back of the book the pupil will find a glossary that gives the pronun¬ 
ciations and meanings of many of the more difficult words. 

2 The lighter portion of the protoplasm is called cytoplasm. 

3 A few cells, for example, a frog’s egg, are large enough to be seen with the 
naked eye. In general, however, cells are very small; so small that it would 
require twenty-five hundred cells from the human body to make a row an inch 
long. 


THE HUMAN BODY A COLONY OF CELLS 


5 


mud. Fifty years ago, many physicians and other scientific 
men believed that disease germs and other little microbes 
were formed from unclean and decaying matter, and many 
persons still think that this is true. 

We know now that all these ideas are incorrect. All living 
things, from the smallest germ to the greatest whale, are 
made of cells, and a cell can come, not from dead matter, 
but only from another living cell. 



Fig. 2. Cell division. The nucleus of the cell divides and part goes to each end 
of the cell. A wall is formed across the cell, dividing it into two parts, each of which 
is a cell. All new cells are formed in this way. 

The nucleus of a cell divides, and part of it goes to each 
end of the cell. Then a wall forms across the cell, and 
divides it into two parts. Each part is a new cell with its 
own nucleus, and each part grows as large as the parent 
cell. All new cells are formed in this way. “ Every cell 
comes from a cell.” 

One-Celled and Many-Celled Animals. In a drop of stag¬ 
nant water many hundreds of little animals may sometimes 
be found, — animals so small that you can see them only 
with a microscope. One of these little animals has only one 
cell in its body. The animal is a single cell that swims 
about alone and lives by itself. When this cell divides, the 
two new cells separate, and each one forms a new animal. 







6 


HUMAN PHYSIOLOGY 


The bodies of all the larger animals (for example, the 
body of the chick in an egg) begin with a single cell, but 
when this cell divides, the new cells do not separate, like 
those of the one-celled animals. The cells remain together 
and keep on dividing and dividing until, in the body of a 
large animal, like a man, there are millions and millions of 
cells, — more than you could count in many years. The 

CILIA 


Fig. 3. A one-celled animal dividing. This cell swims about in the water by 
means of small hair-like cilia which beat the water. When it divides, the new cells 
separate instead of remaining together as they do in the many-celled animals. 

difference between the little one-celled animals and the larger 
many-celled animals is therefore this: in one-celled animals, 
the cells separate after they divide and each cell lives alone. 
In the many-celled animals, the cells remain together after 
division, and live in a great colony. 

Your body, therefore, is a great colony of cells, and each 
cell in it corresponds to an entire one-celled animal. You 
might almost think of yourself as made up of a great com¬ 
munity of little animals, yet this idea would not be wholly 
correct. The cells of our bodies have learned to live to¬ 
gether. They would die if separated, and it takes them all 
to make one complete animal. 




THE HUMAN BODY A COLONY OF CELLS 


7 


Different Kinds of Cells do Different Kinds of Work. The 

single cell of a one-celled animal must do many different 
kinds of work to live. It has no hands to get food for it, 
no teeth to chew the food, and no stomach to digest it. It 
has no lungs to breathe in oxygen, and no kidneys to throw 
off its poisonous wastes. It lives all alone, with no other 
cells to help it, and it must do everything for itself. Each 
cell in the human body has the same needs as the little 
animal cell which lives alone. Each must have food, must 
get oxygen from the air, and must get rid of its poison¬ 
ous wastes. Many of our cells are shut up in the center 
of the body, where they can get neither food nor oxygen for 
themselves, and their waste matter would poison both them¬ 
selves and their neighbors if there were not some way of 
getting it entirely out of the body. Each cell cannot 
take care of itself, as does the little animal in the drop of 
water. 

You can easily see how much it would be to the advantage 
of all the cells in the body for each one to give up trying 
to do everything for itself, and for all. of them to unite and 
work for the good of the whole community. This they have 
done. They have divided the work, and 
each cell has taken for its own some special 
task. The cells of the stomach digest the 
food ; the bone cells build up a strong frame¬ 
work to support the body ; the muscle cells 
move the body; the kidney cells throw out 
wastes; the lung cells take in oxygen from ach. The function 

the air; and the cells of the blood (red blood ( wor ^) of these ceils 
7 v is to digest the food. 

corpuscles) carry oxygen through all the 

body to the cells. Each cell is a skilled workman doing 

some particular work for the body as a whole, and not 



Fig. 4. Cells from 
a gland of the stom- 






Connective tissue. In its first stage 
connective tissue is a group of cells 
which build around themselves a mass 
of jelly-like material, as shown in A. 
This material hardens into the fibers 
that are seen between the ceils in D. 
All through the body a framework of 
connective tissue runs, holding the cells, 
organs, and tissues in place. 



One of the 
nerve cells 
from the 
brain. These 
cells are asso¬ 
ciated with 
thought. 



Cells of the outer 
layer of the skin. 
These cells form a 
protective covering 
for the body. The 
outer cells die and 
dry up until they are 
mere scales. 



A muscle cell from the stomach. The 
muscle cells have the work of moving the 
body. 



Bone cells. These much-branched cells 
deposit around themselves bone material 
(b ), thus building bones to support the body. 
The bone cells build a network of fibers like 
dense connective tissue and then fill the 
spaces between the fibers with hard mineral 
matter. a is a cavity from which the bone 
cell has been removed. 



Fat cells. Food for the body is stored in 
these cells. Large quantities of fat collect 
in the cell, and crowd the protoplasm (a 
and b ) to one side. A fat cell is little 
more than a bag of oil. 


Fig. 5. Cells from the human body. Each kind of cell in the body has a 
particular work to do for the body as a whole. 


S 














THE HUMAN BODY A COLONY OF CELLS 


9 


an unskilled laborer trying to do all the many different kinds 
of work necessary to provide for its own wants. 

The Cells Dependent on Each Other. You will now under¬ 


stand that the cells in the body must depend on each other for 
many things. If the stomach fails to digest the food, there 
will be a lack of food in all the cells. If the kidneys do not 
throw off the wastes, all the cells will be poisoned. If the 
lungs stop taking in oxygen, all the cells must die for lack 
of oxygen. If part of the cells fail in their work, all the 
cells must suffer, and death usually comes to the body because 


part of the cells have ceased to work. 

The Body compared to a Community. The resemblance 
between the body and a community of people must now 
be very clear to you. In both the body and the com¬ 
munity we have individuals, each leading his own life and 
yet making a part of a greater whole. In 
the community we have individuals of dif¬ 
ferent occupations, — doctors, teachers, car¬ 
penters, blacksmiths, grocers, and milkmen. 

In the body we have, as we have seen, cells 
of different kinds,—muscle cells, bone cells, 
digestive cells, and many others. In both 
the body and the community the individual 
does not provide everything that he uses, 
but depends on others for many things. 

The carpenter builds houses for the milk¬ 
man and the grocer, and these persons 
bring the carpenter his food. The stom¬ 
ach cells digest food for the cells of the 
lungs, and the lung cells take in oxygen 
for the stomach cells. 



FIG. 6. Cells from 
the lining of the tra¬ 
chea. a is a cell that 
manufactures sticky 
mucus ( b) in which dust 
and germs from the air 
are caught. The cilia 
(c) on the other cells 
beat upward and sweep 
the mucus, dust, and 
germs up out of the 
air passages and lungs. 


Communities are prosperous and the body is healthy only 



10 


HUMAN PHYSIOLOGY 



Fig. 7. Cells from the blood. 
A is a white corpuscle whose 
function is to kill disease germs; 
Z?isan edge view and Cis aside 
view of the red corpuscles that 
carry oxygen through the body. 


when the individuals do their work faithfully and well; for 
no person in a community lives to 
himself, and no cell in the body lives 
to itself, but each has a share in the 
life of all. New individuals from time 
to time are born into the community 
and other individuals die. New cells 
are constantly being formed in the 
body, and every day millions of cells 
in the body are destroyed. Com¬ 
munities increase in size when the 
number of births in them exceeds the number of deaths, and 
the body grows when the number of new cells formed in it is 
greater than is the number of the cells that die. Thus in 
many ways the body resembles a community of people where 
each individual is doing something for the good of all. 

Tissues. If you have now in mind what has been said 
about cells and their work, you will have no difficulty in 
understanding what is meant by tissues. In a factory we 
usually find the workmen who do the same kind of work all 
collected in one part of the factory. So in the body we. 
usually find grouped together the cells which do the same 
kind of work. The great group of nerve cells is in the brain. 
The muscle cells are collected in the muscles, and the kidney 
cells in the kidneys. Where cells of one kind are grouped, 
a tissue is formed, so we may say that a tissue is a group of 
cells which do the same kind of work. Muscle tissue is 
made of muscle cells, fatty tissue of fat cells, and nerve 
tissue of nerve cells. Each tissue is a group of cells which 
do some particular work for the body as a whole, and in 
return have many things done for them by the cells of other 
tissues. 


THE HUMAN BODY A COLONY OF CELLS u 

Organs. An organ is a part of the body that does a special 
work. The kidney is an organ for throwing out wastes, the 
lungs are organs for taking in oxygen, the eye is an organ 
for seeing, and the stomach is an organ for storing and digest¬ 
ing food. Some organs, like the liver, the kidneys, and the 
heart, are chiefly of one kind of tissue. Other organs have 
in them many kinds of tissues. The hand is an example 
of an organ of this kind, bone, connective tissue, muscle, and 
skin all being united in it to form an organ for grasping. 

Why you should understand the Cell. It is very impor¬ 
tant for you to understand the cell, because a clear idea of 
the cell will give you a new way of thinking about all 
living things. Having an understanding of it, you will 
not only think of an animal as a living thing, but you will 
also think of the millions of cells in its body, each filled 
with living protoplasm. When you see a plant cut down, 
or an insect, or a frog, or a bird killed, you will not only 
think of how the plant or animal dies, but you will think 
of how all the little cells in its body also die; and from 
thinking of the living objects about you in this new way, 
you will become interested in many things which you do not 
now notice, and will understand much that now seems strange 
to you. When you see a rose living for several days after it 
has been cut from the bush and placed in water, or when 
you see a branch of a plant living and growing when placed 
in the soil, you will know that when a part of a plant is cut 
off from the body of the plant, its cells need not always 
die. If you read that when a starfish, or certain kinds of 
worms, are cut into pieces, each piece grows into a complete 
animal, you will see that in these animals, as in plants, 
the cells are more independent than in the human body, 
and that a group of them is able to live without the rest of 


2 


HUMAN PHYSIOLOGY 


the body. Also, when you learn to think of animals as groups 
of cells, you will not wonder that a frog’s legs should twitch 
and jerk in the skillet; or that after the head has been cut 
off, a snake’s tail can live and move, and a turtle can walk 
about. For you will understand that in these animals, as 
in the rose, part of the cells can live for a time without the 
others, and that the muscle cells are living and moving after 
the brain cells are dead. All these things and many others 
you can clear up for yourself, if you will think about the 
cell instead of about the body as a whole. 

A second very important reason why you should under¬ 
stand the cell is that you may intelligently care for your own 
bodies. Each of the great multitude of cells in your body is 
following out its own little life, and each is industriously work¬ 
ing for the good of the community in which it lives. We 
hope that you will understand that your cells must have 
proper food, oxygen, exercise, and rest, and that they must 
get rid of their waste matter. You should realize that any 
medicine you take can act on the body only by being carried 
by the blood through the body and entering the living proto¬ 
plasm of the cells. If it helps the cells, it is beneficial to the 
body, and if it injures the cells, it injures the body. You 
should understand how reckless it is to take in among all these 
delicate cells patent medicines, headache remedies, alcohol, or 
tobacco, unless you are perfectly certain that these things will 
not harm the cells. For the cells of your body are the most 
important things in all the world to you. If they become 
diseased, you will fall sick; and if they fail in their work, your 
life must cease. When the bricks crumble, the house falls; 
and when the cells are dead, the body is dead, for the life is 
in the cell. 

There is a third reason why you should understand the 


THE HUMAN BODY A COLONY OF CELLS 


13 


cell, and that is because in physiology we constantly study the 
work of the different kinds of cells. If you did not under¬ 
stand the figures 1, 2, 3, and 4, you would get very little 
pleasure or profit from trying to solve problems in arith¬ 
metic; and if you do not understand what a cell is and 
how the body is made up of cells, you will think that physi¬ 
ology is a dull subject indeed, and it will never mean much to 
you. But understanding the cell, you can study the differ¬ 
ent parts of the body intelligently, and in all the world you 
will find nothing more wonderful or interesting than your 
own body. 

Anatomy, Physiology, and Hygiene. Anatomy is the study 
of the structure of the body ,— the study of the way all its 
organs are composed of tissues and its tissues made of cells, 
and of how all the organs and tissues are joined together to 
make one body. Physiology is the study of the function of 
the different cells , tissues , and organs , —the study of the work 
which all the different parts of the body do. Hygiene is the 
study of how to keep the body in health. These three subjects 
we must study in this book. 

Summary. The human body, like all other living things, 
is composed of cells. Each cell is a little piece of protoplasm 
that takes in food and grows and is alive. Cells are formed 
only by the division of other cells, and living things can come 
only from other living things of the same kind. They can¬ 
not come from dead matter, although this has often been 
believed. 

When a one-celled animal divides, the new cells separate. 
In many-celled animals the cells remain together after divi¬ 
sion, and the bodies of the larger animals are great colonies 
of cells. Each cell of the human body corresponds to an 
entire one-celled animal. Each cell in the body, like a one- 


14 


HUMAN- PHYSIOLOGY 


celled animal, must have food and oxygen and must get rid 
of its wastes. 

It would not be possible for a cell in the body to supply 
all of its own wants, so each cell spends all its time in one 
kind of work, and depends on other cells for many things 
that are necessary to its life. It follows, therefore, that when 
part of the cells in the body fail in their work the whole body 
must die. The division of labor among the cells causes the 
body in a striking way to resemble a community where the 
people have different occupations and each one has many of 
his wants supplied by others. 

As the workmen who do the same kind of work in a fac¬ 
tory are often found together, so the cells that do the same 
kind of work in the body are found in groups. Such a group 
of cells — cells that do the same kind of work — is called a 
tissue. An orga?i is a part of the body that, like the hand or 
the eye, is fitted for some special work. It may be composed 
chiefly of one or of many kinds of tissues. 

A clear idea of the cell is a very great help in understand¬ 
ing all living things, in caring for our own bodies, and in the 
study of physiology. Anatomy is the study of the structure 
of the body, Physiology is the study of the function of the 
different organs of the body, and Hygiene is the study of 
how to keep the body in health. 

QUESTIONS 

Of what is the human body composed ? Describe or draw a cell. 
What kind of objects are composed of cells? How are new cells 
formed? Where do living things come from? Give some of the 
beliefs that have been held by different people in regard to the ori¬ 
gin of animals and plants. Describe the process of cell division. 


THE HUMAN BODY A COLONY OF CELLS 


15 


In a one-celled animal what do the cells do after division ? What 
do the cells do after division in a many-celled animal ? What in the 
human body corresponds to an entire one-celled animal? What are 
some of the needs of a cell? 

Explain why a cell in the body could not provide for all its own 
wants. Name some of the different kinds of cells in the body and 
explain the function (work) of each. What happens to the body if 
part of the cells fail in their work? Give examples of cells that 
must do their work to keep the body alive. Mention some ways in 
which the body corresponds to a community of people. 

What is a tissue? Name some of the body tissues. What is an 
organ? Name some organs of the body and give their functions. 

Give three reasons why it is important to understand the cell. 

What is Anatomy? Physiology? Hygiene? 

If a cell and a peach were compared, what part of the cell would 
correspond to the seed of the peach? to the flesh of the peach? to 
the skin of the peach ? 

In an egg there is one living cell lying on the side of the yolk. 
What is necessary to make this cell grow and divide ? Of what use 
are the yolk and white of the egg to the cell within the egg? Into 
what have the yolk and the white been changed by the time the egg 
hatches? 

Does the cell in a duck’s egg grow into a duck and the cell in a 
hen’s egg into a chick because the food supply in the eggs is different, 
or because the living cells in the eggs are different? Are the cells of 
your body always composed of the same materials, no matter what 
kind of food you eat? 

Can a branch be transferred from one tree to another and still 
live? Can a piece of tissue be transferred from one person to an¬ 
other? Ask a physician if cells from the body of an animal can be 
transplanted to the human body. 

What happens in a wound when it heals? Ask a physician how 
the cells in a scar differ from the cells in other parts of the skin. 



CHAPTER II 




THE PLAN OF THE HUMAN BODY 


DORSAL CAVITY 


THORACIC CAVITY 


VENTRAL CAVITY 


The human body is com¬ 
posed of a head, a trunk, and 
two pairs of limbs. It is sup¬ 
ported by a skeleton, the most 
important part of which is the 
spinal column , or backbone. 
In the head are eyes, ears, a 
nose, and a mouth. The body 
has in it two cavities, a dorsal 
or back cavity, and a ventral 
or front cavity. In these two 
cavities are found most of the 
organs of the body. 

The Dorsal Cavity. In the 
head is a great cavity, and 
opening out of this cavity at 
the base is a long passage¬ 
way that runs through the 
spinal column from top to 
bottom. The cavity in the 
fig. 8. The cavities of the body. The head and the canal in the 

dorsal cavity is in the head and the spinal backbone, taken together, are 
column. The ventral cavity is in the front . 

of the trunk and is divided by the diaphragm the doi Sal Cavity. Ill this 
into an upper and a lower part. cavity lie the great centers of 

the nervous system, the brain and the spinal cord . 

1 The name dorsal comes from dor 1 sum, the Latin word for back. In the lower 
animals it is easy to see that the cavity in the head and the canal in the spinal 


ABDOMINAL CAVITY. 




THE PLAN OF THE HUMAN BODY 


17 


The Ventral Cavity. The ven¬ 
tral cavity is a great hollow in 
the front part of the trunk. 

Stretched across it is a thin 
sheet of muscle, called the dia¬ 
phragm, which divides it into an 
upper and a lower part. The 
upper part is the chest or thoracic 
cavity. It contains the heart 
and lungs and many of the great 
blood vessels. The lower part 
is the abdominal cavity. In the 
left side of this cavity, its outer 
end close up under the dia¬ 
phragm, lies the stomach. On 
the right side of the body and 
partly covering the stomach 
is the liver. The intestine is 
very long and is coiled again 
and again in the abdominal cav¬ 
ity, filling most of it. Attached 
to the back walls of the cavity 
are the two kidneys, which 
take waste matter out of the 
body. At the left end of the 
stomach is a dark red organ called the spleen. Along the 
lower back part of the stomach is the pancreas , a very im¬ 
portant digestive organ, whose work we must take up in 
another chapter. 

Man’s Place in the Animal Kingdom. Man has a spinal 



FlG. 9. Section of the body show¬ 
ing the positions of the organs in the 
cavities. 


column are all part of one long cavity that runs along the back of the body and 
widens out at the head end to make room for the brain. 







i8 


HUMAN PHYSIOLOGY 



column, and therefore 
belongs among the ver¬ 
tebrates} or backboned 
animals. He has hair, 
and when young lives 
on milk, and therefore 
he belongs among the 
mammals , the highest 
class of the vertebrates. 
The five classes of ver¬ 
tebrates are the fishes, 
amphibians, reptiles, 
birds, and mammals. 
By studying Figure u, 
you can learn some of 
the animals that belong 
in each class, and which 
animals are closely 
related to man. 

The Bodies of Verte- 
A fish, a frog, a lizard, a bird, and a cat do 


HEA.TT 


LUNG 


DIAPHRAGM 


FIG. io. The organs in the ventral cavity, seen 
from the front. 


brates Similar. 


1 The vertebrates differ from worms, insects, and other lower animals in having 
backbones. The five classes of vertebrates have the following distinguishing 
characteristics: 

Fishes live in the water and breathe by means of gills. 

Amphibians have sticky skins, and both lungs and gills. ' Some salamanders 
have lungs and gills at the same time and can breathe either in the water or in 
the air. Other salamanders have gills at one time and lungs at another. Frogs 
and toads have gills in their early life and lungs in their later life. 

Reptiles have scaly skins and breathe by means of lungs. Like the fishes and 
amphibians, reptiles are cold blooded. 

Birds have wings and a body covering of feathers. 

Mammals have the body partly or entirely covered v/ith hair and feed their 
young with milk. The mammals and birds are warm blooded. 





Fig. ii. The vertebrate animals. Man stands at the head ot the mammals, the 
highest class of the vertebrates. 

*9 










20 


HUMAN PHYSIOLOGY 


not seem much alike; and because man walks upright, the 
human body seems very different from the bodies of all these 
animals. Yet man and all other vertebrate animals are built 
on the same general plan. 

Like man, all the vertebrate animals have a head and trunk, 
with eyes, ears, and a mouth in the head. All of them have 
a dorsal and a ventral cavity in the body, with in general the 
same organs in these cavities as are found in man. All have 
skeletons resembling the human skeleton, not only in the 
spinal column, but also in many other parts, as we shall see 
later. All of them have two pairs of limbs corresponding to 
the arms and the legs of man. In a fish, the limbs are the two 
pairs of fins found on the sides of the body. In the seal 
and the whale, they are paddles for swimming. In most 
other animals, they are the fore and hind legs, but in bats 
and birds the fore limbs are wings, and in man they are arms. 
Most snakes have lost their limbs, but in some of the great 
snakes the remains of little legs can be found, and in other 
reptiles the limbs are well developed. 

How Man differs from Other Vertebrates. The brain of 
man is better developed than is the brain of any other animal, 
and in many ways the human body differs to a certain extent 
from the bodies of other vertebrates. But the great difference 
between man’s body and the bodies of other animals is that 
man is built to walk erect. Instead of carrying the head 
in front of the body and walking on all four limbs in the 
position that a fish is in when it swims or a cat is in when it 
walks, the human body stands on the hind limbs, with the body 
erect and the head above the body. When the body stands 
upright the fore limbs do not touch the ground. Therefore, in 
man the fore limbs are not fitted for walking, but are arms 
and have hands for grasping. 


THE PLAN OF THE HUMAN BODY 


21 


Summary. The human body is composed of a head, a 
trunk, and two pairs of limbs. It has in it a dorsal and a ven¬ 
tral cavity. The dorsal cavity contains the brain and the 
spinal cord; the ventral cavity is divided by the diaphragm 
into the thoracic cavity and the abdominal cavity. The tho¬ 
racic cavity contains the heart, the lungs, and many great 
blood vessels. The abdominal cavity contains the stomach, 
intestine, liver, spleen, pancreas, and kidneys. 

Animals with backbones are called vertebrates. Vertebrates 
are divided into five classes, — fishes, amphibians, reptiles, 
birds, and mammals. Man has a backbone, and is a verte¬ 
brate. He has hair, and when young lives on milk; he is 
therefore a mammal. 

The bodies of other vertebrates are built on the same plan 
as the human body. Every vertebrate has a head, trunk, 
eyes, ears, and a mouth. In the body are a dorsal cavity and 
a ventral cavity. It has a skeleton with a backbone, and has 
two pairs of limbs corresponding to our arms and legs. 

Man’s body differs from other vertebrate bodies chiefly in 
that it stands erect. The fore limbs do not touch the ground 
in walking, and are arms with hands. 


QUESTIONS 

Name the principal divisions of the human body. How is the 
body supported ? What two cavities are in the body ? 

Where is the dorsal cavity? What does it contain? Into what 
two parts is the ventral cavity divided? What is the partition be¬ 
tween these parts called? Name the organs in the thoracic cavity; 
in the abdominal cavity. Locate the stomach. Locate the liver. 

Name the five classes of vertebrates. To which class does man 
belong? How does this class differ from other vertebrates? 


22 


HUMAN PHYSIOLOGY 


Give four ways in which the bodies of all vertebrates are similar. 
Mention some different kinds of vertebrate limbs. How does man 
differ from other vertebrate animals? 


What animals do you know that are not vertebrates? Can you 
name an animal that has no head ? one with no mouth ? one with no 
eyes? one with no ears? Name some animals that differ from verte¬ 
brates in the number of their limbs. 

How does a fish differ from other vertebrates? What is the dif¬ 
ference between a shark and a true fish ? How does an amphibian 
differ from other vertebrates? a reptile? What are the four reptile 
groups? What do you know about the reptiles that lived in former 
ages of the world ? 

Which is the lowest mammal shown in Figure it? In what way 
is this mammal like birds and reptiles, and different from the mam¬ 
mals of other groups? How do marsupials differ from other mam¬ 
mals? In what country is the sloth found? Name some mammals 
that live in the water. Do these mammals have lungs or gills? On 
what do the ungulates (hoofed animals) feed? On what do the 
carnivora feed? the primates? 

Can you name some relative of the seal? Where do most of the 
weasel family live and what is obtained from this group of animals? 
Name some members of the cat family not shown in Figure n ; of 
the dog family. What small North American animal is closely 
related to the bears? Name some rodents (gnawers) that are larger 
than any of the rodents shown in Figure n. Draw in a larger form 
the ungulate branch of the vertebrate tree, putting on it all the 
hoofed animals that you know. Do you know any families of mam¬ 
mals not shown in Figure j i ? 



CHAPTER III 


THE RULER OF THE BODY 

All parts of the body must be controlled and made to 
work together. Over them all a ruler must be set. Not 
only must the different organs be kept at work, but each 
must be made to do the proper amount of work, and to do 
it at the right time. If the digestive organs should begin 
to work when nothing had been eaten, their work would 
be useless. If the sweat glands should begin to pour out 
sweat on the skin when the body was not hot, their work 
would be not only useless, but even harmful. If all the 
muscles should begin to pull and jerk without any order 
or system (as they do in convulsions), they would succeed 
only in throwing the body to the ground. 

The ruler of the body is the nervous system. When we 
walk, it is the nervous system that causes the right muscles 
to move. When we eat, the nervous system sets the diges¬ 
tive organs to work. It keeps the heart and lungs going, 
and governs all the body. The function of the nervous sys¬ 
tem is to govern all the organs of the body , and to cause them 
all to work together for the common good. 

The Divisions of the Nervous System. The nervous sys¬ 
tem has two great divisions, — the central nervous system 
and the sympathetic nervous system. The great centers of 
the central nervous system are the brain and the spinal 
cord. The central nervous system controls the voluntary 

23 



Fig. 12. The nervous system. From the brain and spinal cord, nerves run 

to all parts of the body. 

24 


1 





THE RULER OF THE BODY 


25 


muscles (those which we can move when we wish), and its 
higher centers act as the organ of the mind. 

The sympathetic nervous system controls the glands 1 of 
the body and the involuntary muscles (those which we can¬ 
not control by the will, as the muscles of the stomach, intes¬ 
tine, heart, and blood vessels). 

The Brain and the Spinal Cord. The brain has three divi¬ 
sions,— the cerebrum , the cerebellum , and the medulla oblon¬ 
gata. The spinal cord is the soft white substance that you 



Fig. 13. The brain. 


may have seen in the backbone of an animal. In the back^ 
bone of a man it is a little thicker than a lead pencil. At the 
base of the skull is a great opening, through which the spinal 
cord enters the cranium (page 34) and joins the brain. 

The Membranes of the Brain and Cord. Around the brain 
and cord are three connective tissue membranes. The 
outermost membrane, which is thick and tough, is called 

1 The salivary glands, glands of the stomach and intestine, the pancreas, liver, 
kidneys, and sweat glands are some of the glands in the body. 




26 


HUMAN PHYSIOLOGY 


the dura mater . It lines the entire dorsal cavity of the 
body, both the cavity of the cranium and the cavity in the 
spinal column. The innermost membrane, which is thin and 
delicate, is called the pia mater. It lies close to the surface 
of the cord and brain and dips down into all the wrinkles 
and folds in the surface of the brain. In it are the blood 
vessels that nourish the outer parts 
of the brain and cord. Between 
the dura mater and the pia mater 
is a third membrane, the arachnoid 
membrane. These membranes 1 
hold the very soft and delicate 
brain and cord in place and keep 
them from being shaken about 
within the dorsal cavity. 

The Cerebro spinal Fluid. The 
brain and spinal cord are still 
further protected by a layer of 
liquid around them called the cere¬ 
brospinal fluid . This fluid is under 

showing the opening through t h e arachnoid membrane — that is, 
which the spinal cord enters the* 

cranium. between the arachnoid membrane 

and the pia mater — and entirely 
surrounds the cord and brain. It acts as a cushion inside the 
walls of the dorsal cavity and keeps the brain and cord from 
striking against the walls of the cavity. 

Nerves. From the under surface of the brain and from the 
spinal cord, shining white nerves pass out to every part of 
the body. If you should examine one of these nerves under 

1 The three membranes taken together are called the meninges of the brain 
and cord. Cerebrospinal meningitis is a disease caused by germs growing in 
these membranes and in the cerebro-spinal fluid. 



Fig. 14. . The base of the skull, 



THE RULER OF THE BODY 


2; 


a microscope, you would find that it is made of many hun¬ 
dreds of very fine fibers, bound together by connective tissue. 
Although these fibers are so slender that they cannot be seen 
without a microscope, some of them are of great length, the 
longest reaching from the spinal cord to the hands and feet. 

In the larger nerve trunks the fibers are bound up in a 
number of bundles, which are all wrapped together in a com¬ 
mon sheath (Fig. 15). The larger nerves divide into smaller 



Fig. 15. A is a cross-section of a nerve, showing the bundles of nerve fibers that 
make up the nerve, wrapped in the connective tissue sheath. B is one of the bundles 
of nerve fibers shown in A, enlarged to show the individual fibers. 


branches containing only a few bundles, or sometimes only 
one bundle. In the finest nerve branches, the bundles of 
nerve fibers finally break up into the separate fibers, many 
thousands of which end in the skin and muscles, and in the 
other organs of the body. 

The Function of Nerves. The function of the nerves is to 
carry messages between the different parts of the body and the 
brain and spinal cord . 

Some nerves carry messages to the brain and cord. By 
these messages we learn when anything touches the body, 



28 


HUMAN PHYSIOLOGY 


when the body is hungry or thirsty, or hot or cold, when it 
is in pain, and about the things that we see, hear, taste, and 
smell. Other nerves carry messages outward from the brain 
and cord, causing the muscles to move, and making all the 
parts of the body to work together in harmony. The power 
by which we feel, think, and will lies in the brain. The 
commands that we send out, causing voluntary movements 
of the muscles, start from the brain. The nerves are useful 
only to carry to the cord and the brain messages which tell 
us about the body and the outside world, and to carry com¬ 
mands outward from the brain and cord to the muscles and 
to the other organs of the body. 

The Telegrapher and the Telegraph Wires. The brain and 
spinal cord are often compared to a telegrapher in an office, 
and the nerves in the body to telegraph wires that run out 
in all directions from the office. Over the wires the tele¬ 
grapher receives messages that tell him what is going on 
about him, and he sends out messages commanding that cer¬ 
tain things be done. So through some of the nerves the 
brain and cord receive messages which tell them about the 
body and the things going on around it; and over other 
nerves they send messages out commanding the muscles to 
move the body, and the different organs to do their work 
according to the body’s needs. 

Necessity for a Nervous System. From this you will under¬ 
stand that the nervous system connects all parts of the body 
and causes all the organs to work together for the good of 
the body as a whole. Without a nervous system, the human 
body would not be one body at all, but a mass of flesh and 
blood and bones, the different organs working not at all, or 
working without plan or system, and the whole body certain 
to die in a few minutes. With a nervous system it is the living, 


THE RULER OF THE BODY 


29 

moving, speaking human body, the most wonderful thing 
in all the world. 

Summary. The nervous system controls all parts of the 
body and causes them to work together. The great divisions 
of the nervous system are the central nervous system and the 
sympathetic nervous system. The central system controls 
the voluntary muscles; its chief center (the brain) is the 
organ of the mind. The sympathetic system controls the 
involuntary muscles and the glands of the body. 

The brain has three divisions — the cerebrum, the cere¬ 
bellum, and the medulla oblongata. Around the brain and 
cord, and protecting them, are three membranes — the dura 
mater, pia mater, and arachnoid membrane — and a layer of 
cerebro-spinal fluid. 

Nerves are composed of nerve fibers. Nerve fibers carry 
messages between the different parts of the body and the brain 
and spinal cord. Some fibers take messages to the brain 
and cord, and some fibers carry messages away from the 
brain and cord. The nerve centers (brain and cord) may be 
compared to a telegrapher, and the nerve fibers to telegraph 
wires. The incoming messages bring information about the 
body and the world around the body, and the outgoing 
messages are commands from the nerve centers to the 
muscles, glands, and other organs. 

Without a nervous system the different organs of the 
human body would work without system, or would not work 
at all, and the body would die. By the nervous system, all 
the body parts are made to work harmoniously together,— 
all are united into one wonderful body. 


30 


HUMAN PHYSIOLOGY 


QUESTIONS 

What is the function of the nervous system? Name the two 
divisions of the nervous system. What are the chief centers of the 
central nervous system ? What is one of the great functions of this 
system? With what part of the nervous system is the mind associ¬ 
ated? What is the function of the sympathetic nervous system? 

Name the three divisions of the brain. Name the three mem¬ 
branes that are around the spinal cord and brain. What is the 
function of these membranes? What is between the arachnoid mem¬ 
brane and the pia mater? What is its function? 

Describe the structure of a nerve. How long are the longest 
nerve fibers in the body? What is the function of a nerve? 

In comparing the nervous system to a telegrapher and a tele¬ 
graph system, what part of the nervous system corresponds to the 
telegrapher? What is the function of this part of the nervous 
system? What part of the nervous system corresponds to the tele¬ 
graph wires? What is the function of this part of the nervous 
system ? 

To what part of the body are the incoming messages carried? 
What is the effect of these messages? To what organs are the out¬ 
going messages taken? What is the effect of these messages? 

Why is a nervous system necessary in the body? 


Why is it possible for a tree to live without a nervous system, 
when a man cannot do so? If the cells in the human brain should 
become cold, would they die ? Do the cells in the feet or ears die 
if they.become cold? If a fish should be frozen in the ice, would 
the cells of its brain be killed? Are little one-celled animals killed 
by cold water? Ask a physician which cells in the body are most 
affected by such poisons as strychnin, opium, nicotine (the poison in 
tobacco), and alcohol. 




CHAPTER IV 


THE SKELETON 

The skeleton is the framework on which the body is 
built. The shape of the body, therefore, is determined prin¬ 
cipally by the skeleton. Examine your own body, and you 
will readily understand that this is true. Feel your head, 
and under your hair and skin you will find the bones which 
give the head its form. In the fingers and toes are bones 
which determine whether they shall be long and slender, or 
short and thick. Down the middle of your back you can 
feel a row of bones under the skin, and so through all the 
body you will find bones under the skin and muscles, out¬ 
lining the forms of the different parts. 

The Functions of the Skeleton. The first function of the 
skeleton is to support the body. Without a skeleton, the body 
would be weak and soft, and the head, arms, legs, and trunk 
would fall together in a confused mass. But the bones 
are hard and stiff, and form a strong framework, so that 
each part of the body stays in its proper place, and the whole 
body can stand upright. 

The second function of the skeleton is to protect parts of the 
body that are easily injured. The bones of the head form 
a strong box to protect the brain; the spinal column holds 
the spinal cord safe in the cavity in its center; and the bones 
of the chest protect the heart and lungs. 

3 1 



RIBS 

CARPALBON 

METACARPAL 
BONES 


-TARSAL BONES 

METATARSAL BONES 


Fig. 16. The skeleton of the human body. 
32 


SPINAL COLUMN 


ULNA 


PHALANGES 


FEMUR 


FIBULA 

TIBIA- 


PELVIC BONE 


- SKULL 


PATELLA (KNEECAP) 


HUMERUS 


SPINAL COLUMN 
CLAVICLE 


STERNUM 


PHALANGES 























THE SKELETON 


33 


The third function of the skeleton is to provide a system of 
levers, by means of which the body can be moved . Moving the 
body is the special function of the muscles, and we shall 
take up this subject in the next chapter. But you can easily 
understand that without a skeleton such movements as walk¬ 
ing or raising the arm would be impossible. 

THE PRINCIPAL BONES OF THE SKELETON 



Fig. 17. The skull. 


There are two hundred and six bones in the human skeleton. 
They are divided naturally into three groups. The first group 
contains the twenty-eight bones of the head, the second group 
the fifty-eight bones of the trunk, and the third group the one 
hundred and twenty bones of the limbs. 

The Skull. The twenty-eight bones of the head taken to¬ 
gether compose the skull. Eight of these bones are solidly 





34 


HUMAA r PHYSIOLOGY 


united to form a box (the cranium') for the protection of the 
brain. Six little bones are in the ears (Fig. 120), and the 
other fourteen bones of the skull form 
the skeleton of the face. All the bones 
of the face are in pairs except the lower 
jawbone and the thin bonewhicli forms the 
partition between the two sides of the nose. 

The Spinal Column. The spinal column 
is composed of twenty-four vertebra (sin¬ 
gular, vertebra\ the sacrum , and the coccyx. 
It supports the parts of the body above the 
hips , and protects the spinal cord. When 
it is broken, standing or walking is im¬ 
possible, because the trunk has no support, 
and because the spinal cord, through which 
the muscles that keep the body erect are 
governed, is injured. 

To do its work, the spinal column must 
have strength enough to carry the weight 
of the trunk, head, and arms, and must 
bend easily in all directions, yet not sharply 
enough at any one point to crush the deli¬ 
cate spinal cord within it. If it were com¬ 
posed of long bones, either it would be stiff 
and allow little movement of the upper 
parts of the body, or it would bend sharply 
at the joints as the arms do at the elbows 
and the legs at the knees, and injure the 
Fig. 18. The'spinai C01 *d at ^ ese points. But because the 
column. spinal column is composed of many short 
bones, and has many joints, it allows the body to bend freely 
forward or backward, or from side to side, yielding a little at 



THE SKELETON 


35 


each joint, but not enough anywhere to crush the cord. Also, 
because the spinal column is flexible, bending at so many 
different points, it rarely happens that it is broken, as would 
be the case if the trunk were carried on a stiff support. 


Fig. 19. 


The bones of the trunk. 



The Sternum and Ribs. The sternum , or breast bone, is 
a flat bone lying in the front of the chest The ribs are 
long, slender bones, which curve around the chest. They are 
twenty-four in number. — twelve pairs. All the ribs are joined 








36 


HUMAN PHYSIOLOGY 


to the vertebrae at the back. The seven upper pairs are 
joined to the sternum in front, and are called true ribs. 
The five lower pairs of ribs are called the false ribs. The 
three upper pairs of false ribs have their front ends attached 
to the lowest pair of true ribs. The two lowest pairs of false 
ribs are called floating ribs, because their front ends are free. 
The ribs protect the heart, lungs, stomach, liver, and other 
organs lying in the upper part of the ventral cavity, and form 
a framework to which the muscles that are used in breathing 
are attached. 

The Bones of the Shoulder. The clavicle (collar bone) 
and the scapula (shoulder blade) form the skeleton of the 
shoulder. The scapula lies in the back of the shoulder. In 
its outer end is a socket for the upper end of the arm bone. 
The weight of the arm, and of anything which is lifted by the 
arm, pulls downward on the scapula. The scapula, therefore, 
has powerful ligaments and muscles attaching it to the ribs 
and to the vertebrae, and holding it in place. 

The inner end of the clavicle is joined to the sternum, and 
the outer end is propped against the point of the scapula, 
thus bracing the shoulder. When the clavicle is broken, as 
often happens when one falls on the shoulder, the point of 
the shoulder drops downward and forward. By feeling your 
own shoulder, you can easily locate the clavicle running 
out from the sternum to the point of the shoulder, and the 
scapula, with its bony ridge, in the back of the shoulder. 

The Pelvic Bones. Place your hands on your sides, and 
you will feel the two large, irregular, wide-spreading pelvic 
bones. They are firmly joined to the sacrum behind and to 
each other in front. These three bones with the coccyx form 
the pelvis , which balances on top of the thigh bones, and gives 
a firm support for the upper parts of the body. The lower 


THE SKELETON 


37 


abdominal organs lie within the bowl-shaped pelvis, and are 
partly supported by it, and many great muscles are attached 
to the sacrum and to the pelvic bones. 

The Bones of the Limbs. Each limb has in it thirty bones, 
and the bones of the arms and the legs are very similar (Fig. 
33). Each has a large bone in the upper part, the humerus 
in the arm, and the femur in the thigh. Each has two bones 
in the lower part, the radius and the ulna in the forearm, 
and the tibia and fibula in the leg below the knee. In both 
the wrists and the ankles we find a group of small bones, the 
eight carpal bones in the wrist, and the seven tarsal bones in 
the ankle. In the hand beyond the carpals are five meta¬ 
carpal bones, each bearing a finger, and in the foot beyond 
the tarsals are five metatarsal bones, each bearing a toe. In 
the fingers are fourteen phalanges , and in the toes are four¬ 
teen phalanges. The arms and legs have the same number of 
bones in each, and in their general plan differ only in this, — 
the wrist has one more bone than the ankle, and at the elbow 
there is no bone like the patella (knee-cap), which protects 
the front of the knee. 

SHAPES AND STRUCTURE OF BONES 

Shapes of Bones. The bones of the human skeleton may 
be classified as long and short , flat and cylindrical , and irregu¬ 
lar. This gives us a great variety of shapes, but it is usually 
easy to see some connection between the shape of a bone and 
its function. 

Long bones give motion to distant parts of the body, and by 
means of the long bones great rapidity of motion through 
long distances can be brought about. The bones by which 
the hands and the feet are moved so quickly and so far are 
the best examples of long bones. 


38 


HUMAN PHYSIOLOGY 



Short bones give free movement in various directions 
through short distances, and at the same time give great 

strength. The bones of the 
wrists and ankles and the ver¬ 
tebrae are the best examples of 
short bones. 

Cylindrical bones are found 
where supporting some portion 
of the body is one of the main 
functions of the bone. The 
bones of the limbs, of the 
hands and the feet, and the 
clavicles are cylindrical bones. 

Flat bones are usually either 
protecting bones or bones to 
which many muscles are at¬ 
tached. The sternum and the 
bones of the cranium are flat, protecting bones. The pelvic 
bones and the scapulas are 
bones which are spread out flat 
to give room for the muscles. 

Not only are the flat bones made 
so as to give as much room as 
possible for the muscles, but the 
heads of the long bones are ex¬ 
panded for the same purpose, 
and nearly all bones have eleva¬ 
tions and processes (Fig. 21) to 
which muscles can be fastened. 

This is necessary, for there are over five hundred muscles 
in the body, most of which are attached to the skeleton. 

Irregular bones usually have several functions. A good 


FIG. 20. The scapula. This flat bone 
has many muscles attached to it. The 
ridge strengthens the bone and its end 
provides a point against which the 
clavicle can be propped. 



Fig. 21. Vertebrae. 






THE SKELETON 


39 


example of a bone of this kind is a vertebra. This has a 
round portion which supports the weight of the body; it has 
a flattened ring of bone inclosing and protecting the spinal 
cord; and it has a flat spine behind and processes on the 
sides, to which the muscles of the back are attached. 

Materials in Bone. A dead and dry bone is composed of 
a great network of tough fibers and of hard mineral matter 
that fills in the spaces between the fibers. A bone, there¬ 
fore, has in it two kinds of matter, animal matter (the fibers) 
and mineral matter. About two thirds of the weight of the 
average bone is mineral matter and one third is animal mat¬ 
ter. In childhood there is a smaller proportion of mineral 
matter in the bones, and in old age the amount of animal 
matter is very small. By the following experiments you can 
find out for yourself the proportion of animal and of mineral 
matter in a bone, and the function of each kind of material: 


Weigh a piece of dry bone. Then burn it in a hot fire. Notice 
the smell. The animal matter in the bone is 
burning. When all the animal matter has been 
burned out, the bone will have a grayish color. 

When this is the case, take it out of the fire and 
weigh it again. Of what kind of matter is the 
bone now composed? What proportion of it 
was animal, and what proportion mineral matter? 

Try to bend the bone, and notice how easily it 
crumbles and breaks. What do you think is the 
function of the animal matter? 

Dissolve the mineral matter out of the drum¬ 
stick of a chicken or turkey by soaking it in 
weak hydrochloric acid. 1 Then examine the bone, 
and note that it is the same size and shape as be¬ 
fore. Try to bend it and you will find that it is 
as limber as a piece of rubber. Of what is the 
bone now composed ? What is the function of the 
mineral matter of the bone? 



Fig. 22. A femui 
with the mineral mat¬ 
ter removed. 


1 Any weak acid, or strong vinegar, may be used in this experiment. 


40 


HUMAN PHYSIOLOGY 


From these two experiments you will understand that the 
mineral matter gives to the bones the stiffness and firmness 
which enables them to support the body , and the animal 
matter gives the toughness which keeps them from breaking. 

Structure of Bones. The shafts of the long bones and a 
thin layer on the surface of all the bones are composed of 



Fig. 23. A is a portion of the shaft of a long bone. B is a cross-section of a small 
portion of the same bone more highly magnified, showing more clearly the canals in 
the compact bone and the small cavities ( lacuna ) in which the bone cells lie. 


compact bone. The remainder of the skeleton is composed 
of spongy bone. The spongy bone is filled with small cavi¬ 
ties, like the holes in a sponge. The compact bone when 
looked at with the unaided eye appears solid, but when 
examined under the microscope even this hard bone is seen 
to be full of very small canals. Through these canals the 









































THE SKELETON 


41 

blood vessels reach to every part of the bone, carrying nour¬ 
ishment to the bone cells. 

The Cavities in the Long Bones. To provide room for the 
attachment of all the muscles and to have sufficient strength 
for the support of the body, the bones must be large. At 
the same time it would be objectionable to have very heavy 
bones, for the muscles would find great difficulty in moving 
them about. The small cavities in spongy and compact bone 
assist in decreasing the weight of the skeleton. To lighten 



Fig. 24. Experiment showing that a hollow cylindrical bone is strong. 

it still more, large cavities are hollowed out in the long bones 
of the limbs. That a hollow cylinder is stronger than the 
same material in a solid form, you can prove by the follow¬ 
ing experiment: 

Set a sheet of paper on end and lay a book on it. Will it 
support the book? Fold the paper as tightly as possible, so that it 
will be in the form of a small, solid bone. Will it now support the 
book? Now roll the paper into a hollow cylinder and place your 
book upon it. Will it support a heavier weight than it would before 
it was rolled into this form ? Does it contain any more material or 
is it any heavier? 

Nature uses a hollow cylinder not only in the skeleton, 
but in other structures where she wishes to combine strength 







42 


HUMAN PHYSIOLOGY 


and lightness. Stalks of grasses and grains are hollow, and 
so strong is a wheat stalk that it has a height four hundred 
times as great as its diameter, and carries the heavy head of 
grain without breaking, although it is blown about and bent 
by the wind. Man also uses hollow tubes in the framework 
of bicycles, and in other places where he wants strength 
without great weight. 

Bone Marrow. The large cavities of the long bones and 
the smaller cavities of the spongy bone are filled with bone 
marrow. The marrow in the larger cavi¬ 
ties contains blood vessels, nerves, connec¬ 
tive tissue, and fat. The marrow of the 
spongy bone contains less fat, and in it the 
red corpuscles of the blood are formed. 
Because of the large quantity of fat which 
it contains, the marrow of the larger cavi¬ 
ties is yellow in color; the marrow in the 
spongy bone, because of the large number 
of red corpuscles which it contains, usually 
has a reddish hue. 

The Periosteum. Pick the surface of a 
fresh bone with the point of a knife, and 
you can lift a thin covering or membrane. 
This is the periosteum. It is made of a 
network of connective tissue fibers, closely 
woven together over the surface of the 
bone. Among the fibers of the periosteum 
are many of the blood vessels which carry 
nourishment to the bones, and if the periosteum is destroyed , 
the bone under it will die} 

1 A bone grows in thickness by having layers of new bone material laid down 
on the surface of the bone under the periosteum. 



Fig. 25. Longitudinal 
section of the humerus. 





THE SKELETON' 


43 


Summary. The bones support the body, protect delicate 
organs, and act as levers by means of which the muscles move 
the body. There are 206 bones in the human skeleton, — 28 
in the skull, 58 in the skeleton of the trunk, and 120 in the 
skeleton of the limbs. 

In respect to their shape, bones are classified as long and 
short, flat and cylindrical, and irregular. Long bones give 
rapid motion through long distances. Short bones combine 
strength and freedom of movement. Cylindrical bones are 
supporting bones, and flat bones protect delicate organs or 
have many muscles attached to them. Irregular bones usually 
have several different functions. 

Bones are one third animal matter, which makes them 
tough, and two thirds mineral matter, which gives them 
their stiffness and rigidity. The cavities in the bones help to 
lighten them and at the same time permit them to retain 
sufficient strength to support the body. 

Bone marrow contains fat, blood vessels, connective tissue, 
and nerves. The yellow marrow has in it much fat. The red 
marrow contains less fat, and in it the red blood corpuscles are 
formed. The periosteum carries many of the blood vessels 
that nourish the bone. 


QUESTIONS 

Give three functions of the skeleton. How many bones are in the 
body ? Into how many groups are they divided ? How many bones 
are there in each group ? 

How many bones are in the skull? in the cranium? in the ears? in 
the face? Name some of the bones of the skull. 

How many and what bones are in the spinal column ? Give two 
qualities that the spinal column must have. Give two advantages 
that come from having the spinal column composed of many parts. 


44 


HUMAN PHYSIOLOGY 


Where is the sternum ? How many ribs are there ? What is a 
true rib ? a false rib ? a floating rib ? Give two uses of the ribs. 

Name the shoulder bones. To what is the scapula attached? 
What is the function of the clavicle ? What bones compose the 
pelvis ? Give three functions of the pelvis. Compare the skeletons 
of the arm and of the leg. 

Give four shapes of bones, with the functions of bones having each 
of these shapes. Give examples of bones of each shape. 

What two kinds of material in bone ? What proportion of a bone 
is mineral matter ? animal matter ? What is the function of the 
mineral matter ? of the animal matter ? At what time of life is there 
little mineral matter in the bones ? little animal matter ? 

Where in the skeleton is the compact bone found ? spongy bone ? 
How do compact and spongy bone differ? 

Why is it necessary that the bones should have considerable size ? 
What would be the objection to having large solid bones ? How 
have the large bones been lightened without too greatly weakening 
them ? 

Of what is bone marrow composed ? Where is red bone marrow 
found ? yellow bone marrow ? How does one kind of marrow differ 
from the other? What is the periosteum? What happens to the 
bone when the periosteum is destroyed ? 


Of what is the animal matter in a living bone composed (page 8) ? 
Do the bones of an old person or of a little child bend more easily ? 
Why ? Which breaks more easily ? Why ? Which heals more 
easily after it is broken r Why ? 

Is a hollow iron post as strong as a solid iron post of the same 
size ? How many times as high as its own diameter is the tallest 
smokestack or tower that you know ? 

What part of the skeleton is incomplete in a little baby? 



CHAPTER V 


THE SKELETON (Continued) 

JOINTS 

Each bone can support the part of the body in which it 
is located, but to form a skeleton for the support of the body 
as a whole, the bones must be joined together. The places 
where the bones come together are the joints. These are 
divided into two great classes, — immovable and movable 
joints. 

Immovable Joints. Immovable joints are found in portions 
of the body where movement between the bones is not neces¬ 
sary, and where great strength and firmness are required in 
the skeleton. In the cranium all the bones are solidly joined 
to protect the brain, and the joints are immovable. The joint 
between the two pelvic bones, and the joints between the 
pelvic bones and the sacrum, are other examples of immov¬ 
able joints. All the bones of the pelvis are thus firmly united 
in one solid support for the body. In our own bodies we 
overlook the immovable joints because there is no movement 
at these places, but in a skeleton this kind of joint may easily 
be observed. 

Necessity for Movable Joints. Most of the joints in the 
skeleton are movable. It is necessary that they should be, 
for it is only at the movable joints that the body can bend. 
Without movable joints you could not close your hand; you 

45 


4 6 


HUMAN PHYSIOLOGY 


could not bring your hand to your mouth; you could not sit; 
and you could not walk. Without movable joints it would 
not be possible for one part of the body to-be moved without 
moving the whole body. You will understand, if you think 
about it, that with the whole skeleton united solidly in one 
piece, our muscles could not move the body at all. With a 
skeleton having movable joints, they lift the body about, one 
part at a time; but without the bending at the joints, the 
muscles would have no more power of lifting the body than 
you have of lifting a chair in which you are sitting. 

Kinds of Movable Joints. Movable joints are of three 1 
principal kinds,— ball-and-socket joints, hinge joints, and 
gliding joints. 

In ball-and-socket joints a ball, or rounded end, of one bone 
fits into a socket, or cup-like hollow, in the other bone. The 
shoulder joint and the hip joint (Fig. 27) are good examples 
of ball-and-socket joints. This kind of joint allows motion 
freely in any direction, as you can observe by swinging the 
arm about at the shoulder, or the leg at the hip. 

Hinge joints do not allow motion in all directions, but only 
in two opposite directions, — the same movement that a knife 
blade has in opening and closing. The elbow and knee joints, 
the first two joints of the fingers and toes, and the joints of 
the lower jaw are examples of hinge joints. What kind 
of a joint is at the base of the metacarpal bone that bears the 
thumb ? 

In gliding joints the bones move or glide only a little 
on each other. The joints between the small bones of the 
ankles and the wrists are good examples of gliding joints. 

1 The joints between the bodies of the vertebrae are intermediate between im¬ 
movable and movable joints. In them the bones do not slide on each other, but 
the thick and elastic cartilages (Fig. 21) permit considerable bending. 


THE SKELETON 


4 7 


CARTILAGE AND LIGAMENTS 


Cartilage. By far the greater portion of the human skele¬ 
ton is bone, but a small part of it is composed of cartilage 1 and 
ligaments. Cartilage (Fig. 26) is 
a smooth white substance always 
found covering the ends of the 
bones at the joints. In a movable 
joint each bone has its own carti¬ 
lage, and the surfaces where the 
two cartilages rub together are 
kept moist by an oily liquid. The 
smooth cartilage and the oily fluid 
keep down friction in the movable 
joints and cause them to work 
smoothly and noiselessly. 

In immovable joints, a piece of 
cartilage grows in between the 
two bones and firmly unites them. 

Cartilage is found also in the front 
portion of each rib (Fig. 19). This 
makes the ribs more springy and 
less likely to be broken by pressure 
or by a blow on the chest. 

Ligaments. Around the joints are tough bands of con¬ 
nective tissue called ligaments. I11 parts of the body like the 



FiG. 26. Cartilage. Cartilage 
has a connective tissue covering 
(a) similar to the periosteum on 
a bone. The cartilage cells ( 6 ) 
build around themselves a whitish, 
elastic substance ( c ) which forms 
the ground material of cartilage. 


1 When the skeleton is being formed in the body, it is at first composed of 
cartilage. This changes to bone until only a thin layer of cartilage on the ends 
of the bones remains. As long as a bone is growing, however, there is some 
cartilage in it. Thus, in youth, there are in the shaft of a long bone one or more 
narrow rings of cartilage. This cartilage grows and keeps turning to bone on 
each side, causing the bone to increase in length. Finally the rings of cartilage 
turn to bone and there is no more growth in the length of the bone, 


HUMAN- PHYSIOLOGY 


knee, elbow, ankle, and wrist, 
the number of ligaments about 
the joints is astonishingly great. 
Their function is to hold the bones 
of the skeleton together. 

HOW THE SKELETON PROTECTS 
THE BRAIN 

In all ordinary circumstances 
the cranium shields the brain 
Fig. 27. The ligaments Of the hip from outside injury, and the 
J' oint - whole skeleton is arranged to 

protect the brain from injury by jarring. This is necessary 
because the brain is so soft and delicate an organ that not¬ 
withstanding the protection given to it by the membranes 
and fluid about it (page 26), it is shaken about and injured 
by any violent jarring of the head. When you have a head¬ 
ache after having bumped your head, the brain has been 
injured; and death sometimes follows a blow on the head, 
even when the skull has not been fractured, because of injury 
to the brain. 





If the head were jarred every time the feet strike the 
ground in walking and running, it would surely be harmful 





THE SKELETON* 


49 




to the brain. To prevent this jarring, the skeleton has in it 
three devices that give springiness to the whole frame. 

The Arch of the Foot. Press on a curved stick or a piece 
of barrel hoop as shown in Figure 28, and notice how much 
springiness the arch gives it. The bones of 
the human foot form an arch on which the 
weight of the body falls when 
the body is in a standing position. 

In walking and running, there¬ 
fore, the arch of the foot acts as 
a spring under the body. 

The Curves of the Spinal 
Column. Strike the floor with 
a straight stick held as in Figure 
30 and your hand will be jarred. 

But strike the floor with a curved 
stick held in the same way, and 
you will find that the curve will 
give a springiness to the stick 
that prevents the hand from being 
jarred. The double curve of the 
spinal column (Fig. 18) makes it 
springy, and so protects the head 
from the jar when the feet strike 
the ground. You can get an idea 
of the usefulness of these curves 
by imagining how much worse 
your brain would be shaken up 
when you run and jump if your head were carried on the 
end of a straight, stiff bone instead of on your spinal column. 1 

1 Jump with the legs held straight and stiff. Then jump with the legs bent 
at the knees, and notice the difference in the amount of jar the body receives. 


Fig. 30. This 
straight stick 
jars the hand. 


Fig. 31. This 
curved stick 
springs down 
and does not 
jar the hand. 






50 


HUMAN- PHYSIOLOGY 


Cartilages. The cartilages between all the joints, but * 
especially the thick cartilages between the vertebrae (Fig. 21), 
act like rubber pads in giving elasticity to the skeleton. If 
you have worn shoes with rubber heels, or have walked on a 
rubber mat, you will know at once how these, cartilages pre¬ 
vent jarring of the brain. 

These three devices, along with the half-bent joints of the 
legs, give springiness to the skeleton and protect the brain. 
How well this work is done, you may know from the fact 
that boys and girls in their play run 
about and jump, and sometimes fall 
so hard that the bones of the body 
are broken, and yet it is not often 
that the brain is injured. 

THE SKELETONS OF OTHER VERTE¬ 
BRATES 

Similarity of Human and Other 
Vertebrate Skeletons. In the skele¬ 
tons of all vertebrates, a spinal 
column and skull are found. All of 
them except the amphibians have 
ribs. Shoulder and pelvic bones to 
which the limbs are attached are 
found in almost all of them. The 
limbs of vertebrates are built on the 
same general plan, but they are used 
in so many different ways that the 
skeletons of the limbs may seem to 
be very different. Certain bones may be much longer than 
they are in man, as the phalanges in the wings of a bat. 



. Fig. 32. 

Skeleton of an orang-utan. 



THE SKELETON 


5 


Often bones may be united as are the tibia and the 
fibula in the frog, and the carpal and metacarpal, and the 
tarsal and metatarsal bones of many animals. Sometimes 
we have the wrong idea of a limb until we study it closely. 
Thus, in the front limb of the horse, the foot corresponds 
to one finger on our hand, the hoof to a finger nail, and the 
one metatarsal is very long, so that what seems to be the 
knee is really the wrist. In birds the tarsal and metatarsal 
bones are united and elongated and in a chicken the ankle 
joint is often thought to be the knee. In some ways the 
limbs of these animals are very different from the limbs 
of man, but all the principal bones in them correspond to 
the principal bones in the human arms and legs. 

Differences between the Human and Other Vertebrate 
Skeletons. Of all the vertebrates, monkeys and apes have 
skeletons most nearly like the skeleton of man. But although 
an ape’s skeleton has in it every bone that is found in the 
human skeleton, yet there is no difficulty in distinguishing 
between the two. 

An ape has less intelligence than a man, and its brain and 
cranium are much smaller. The jaws of an ape are much 
longer and heavier than they are in man, the teeth are 
larger, and the front teeth slant forward. 

The human spinal column has a backward turn at the 
top that causes the skull to balance on top of the spinal col¬ 
umn when the body stands upright. The spinal column of 
an ape lacks this backward curve, and when an ape stands 
up its head sticks out forward. The muscles of the neck, 
shoulders, and back, therefore, have heavy work to keep the 
head from falling forward when the body stands erect. 

The pelvis and femurs of man are also fitted for an upright 
carriage of the body. Man is a very tall animal for his size, 




PHALANGES 


humerus 


RADIUS 


ULNA 


PHALANGES 


METACARPALS 


HUMERUS 


►TARSALS 


PHALANGES 


TIBIA AND 
FIBULA 


METACARPALS 


HUMERUS 


RADIUS 


ULNA- 


FIBULA 


PHALANGES 


Fig. 33. Vertebrate limbs. A is the human leg; B, the human arm; C, the fore 
leg of a horse; D, the wing of a bird; E, the foot of a bird; F, the hind leg of a frog; 
G, the wing of a bat; H t the fore leg of a tortoise. 


TARSALS AND 
METATARSALS 


CARPALS AND 
METACARPALS 


TIBIA 


* METATARSALS 
. PHALANGES 


FEMUR 


■ RADIUS 






























THE SKELETON 


53 


and he has only two feet to balance himself on. The human 
pelvis is, therefore, wide, and the heads of the femurs are 
turned inward. The feet are thus spread apart, making it 
easier to keep the balance of the body. Shut your eyes and 
stand with your feet wide apart. Then shut your eyes and 
stand with your feet close together, and you will understand 
the advantage of this arrangement. 

The arms of the ape are proportionately much longer than 
the arms of man, and the legs are shorter. In man the arms 
reach about halfway between the hip and the knee. In apes 
they reach to the knee, and in some species even to the 
ground. 

In apes all the metacarpal and metatarsal bones are very 
long except the first one, which is very short. This sets the 
thumbs and great toes far down on the sides of the hands 
and feet, and in reality gives the apes neither true hands 
(with thumbs opposing the fingers) for grasping, nor feet for 
walking, as we find in man; but long organs halfway between 
hands and feet, with which the ape holds to large branches 
as it climbs among the trees. 

HYGIENE OF THE SKELETON 

As the body grows, mineral matter is gradually deposited 
in the bones and the skeleton becomes harder. During child¬ 
hood the bones are flexible and it is easy to bend them and 
change their shapes; but after the skeleton has hardened, it 
is exceedingly difficult to change the shape of the bones. 

It is very important, therefore, that the skeleton be kept 
in proper position during childhood and youth. The general 
carriage of the body cannot be well understood until we 
have studied the muscles, so here we shall point out only 


54 


HUMAN PHYSIOLOGY 


a few ways in which different bones of the body may be 
bent out of their proper shape. 

Allowing a baby to stand up and walk too soon may cause 
him to become bow-legged, and lifting or carrying heavy loads 
may have the same effect on older children. Heavy work 
done by the young is likely to pull the points of the shoulders 
downward and forward, causing round shoulders. Anything 
carried habitually on one side may cause the spinal column to 
be bent over to that side. It has been found that many 
school children have slight curvature of the spine from 
always carrying their books on the same arm, and very 
many people have one shoulder or hip a little higher than 
the other. Boys sometimes wear belts that are drawn too 
tight around the waist, instead of resting on the hips. These, 
or any tight clothing around the waist, may bend in the 
lower ribs. This is very injurious, for it presses on the 
organs which are packed in the abdominal cavity. 

You should avoid all these unhygienic practices, and others 
which you will think of for yourselves, such as stooping 
over your desk, or sitting sideways in your seat with one 
shoulder higher 1 than the other, while you study or write. 
You should take especial care to form the habit of carrying 
the body erect; for if the bones are permitted to harden in a 
stooping position, it is almost certain that you will go through 

1 To the Teacher: Much real damage as well as a great deal of discomfort 
may be caused by having seats and desks that are too low or too high for the 
pupils. Writing on desks that are too high will throw one shoulder higher than 
the other and cause lateral curvature of the spine. Bending over a desk that is 
too low will give a stooping carriage to the body. Sitting in seats so high that 
the feet cannot touch the floor causes stooping and very great weariness. 
Where the school authorities fail to provide proper desks, the teacher should see 
that the younger children have foot rests and should do everything in his power 
to have all his pupils properly seated. 


THE SKELETON 


55 


life with a stooping carriage, your sternum and ribs dropping 
down and crowding your heart and lungs. If you have any 
work that compels you to stoop as you do it, stop once in a 
while, straighten yourself up, and take several deep breaths; 
in addition, make a special point of holding the body erect 
while not at work. 

Broken Bones. If the two ends of a broken bone are 
placed together, the bone cells soon cover the surface of the 
broken ends with a jelly-like, white material. In a few days 
this begins to harden, and soon the two parts are firmly 
united. The only thing we can do to help nature in this 
process is to put the broken ends together, and keep them 
together until the fracture is healed. Of course a physician 
must be called to set a broken bone, but the patient needs 
intelligent care until the physician arrives. If an arm or 
a leg is broken, stretch it out straight on a pillow. If the 
person must be moved, tie a pillow about the limb, or wrap 
a blanket or a coat around it, and then tie umbrellas or canes 
about it to keep it straight. Often there are sharp points on 
the broken ends of bones. In lifting the person, take care 
that the limb is not bent at the fracture , or the sharp ends of 
the broken bone may cut the muscles, blood vessels, or 
nerves. 

Dislocations and Sprains. When the ligaments (and some¬ 
times the muscles and nerves also) around a joint are broken, 
and the bones slip out of place, we have a dislocation. A 
few people have some joints with sockets so shallow that the 
bones may be dislocated without breaking the ligaments, but 
such joints are not common. When a bone is dislocated, it 
must be put back into its place and kept there until the liga¬ 
ments grow again about the joint. Usually only a physician 
can get a dislocated bone back into place without danger to 


56 


HUMAN PHYSIOLOGY 


the patient, and he should be called before the parts become 
swollen. 

When a joint is sprained , some of the ligaments around it 
are broken and torn loose, but the bones are not dislocated. 

Treatment of Dislocations and Sprains. Until a physician 
can be called, both dislocated and sprained joints should be 
bathed in either hot or cold water, or, better still, in hot and 
cold water alternately. This will help to keep the injured 
part from swelling and becoming painful. 

A dislocated or sprained joint should not be rested all the 
time, but should be exercised, even if the movement causes 
great pain. If the joint is not exercised, it will become much 
swollen with liquids from the blood, and will be very painful. 
Exercise helps to keep up a good circulation of the blood 
through the part, and this carries away the broken tissue and 
dead cells, and helps in every way to hasten the healing of 
the injury. But after a dislocation, great care must be used 
that, in exercising, the injured parts are not again dislocated. 
A dislocated joint should be well bandaged to keep the bones 
in place, and then exercised in such a way that there will be 
no danger of dislocating it again. 

Tobacco and the Skeleton. The bones are built up and 
grow through the manufacture of bone materials by the cells 
(page 8). Tobacco seems to injure the cells which do this 
. work, for young persons who use tobacco are usually stunted 
in their growth. We know that tobacco injures the heart and 
the digestive organs, and it may be that it injures the bone cells 
by preventing them from getting a good supply of food and 
oxygen. Possibly the tobacco itself injures the bone cells. 
However the harm is done, we are sure that it is done, for 
the bones of young tobacco users do not grow as they should. 

Summary. There are two great classes of joints, im- 


THE SKELETON 


5 7 


movable and movable. Immovable joints are found in the 
skeleton where motion is not necessary, but firmness and 
strength are required. Movable joints are necessary that the 
different body parts may have motion. The three principal 
kinds of movable joints are ball-and-socket joints, hinge joints, 
and gliding joints. 

The ends of the bones are covered with a smooth, white 
substance called cartilage. In the movable joints this is 
kept moist with an oil-like liquid, which causes the joints to 
work smoothly. At the joints the bones are tied together 
with strong connective tissue ligaments. 

The arch of the foot, the curves of the spinal column, and 
the cartilages in the skeleton and the half-bent knee joints 
keep the brain from being jarred as we walk and run. 

The human skeleton resembles other vertebrate skeletons 
in having a spinal column, skull, ribs, shoulder and pelvic 
bones, and two pairs of limbs. The bones in other vertebrate 
limbs often differ markedly from the bones in the human 
limbs, but in all these limbs the same general plan of the 
skeleton is present. Man’s skeleton differs from an ape’s in 
the skull, spinal column, pelvis, and femurs, the length of 
the arms, and in the hands and feet. 

During childhood and youth the bones are easily bent, and 
it is very important that they be kept in proper position. A 
broken limb should not be allowed to bend,at the fracture. 
In a dislocation or a sprain the ligaments about the joint are 
broken. A joint that has been injured in this way should be 
treated with hot or cold water and carefully exercised. 

Tobacco keeps the bones of the skeleton from reaching 
their full growth. 







58 


HUMAN' PHYSIOLOGY 


QUESTIONS 


What is a joint? What are the two great classes of joints? Where 
are immovable joints found? Give examples of immovable joints. 

Why are movable joints necessary? Name three kinds of mov¬ 
able joints. Explain what movement each kind o*f movable joint 
allows. Give examples of each kind. 

Where is cartilage found? What is its use in the movable joints? 
What is a ligament and what is its function? 

Why is it important that the skeleton should have springiness? 
Name three devices for giving springiness to the skeleton. 

Mention some ways in which the human skeleton resembles other 
vertebrate skeletons. Mention five ways in which the human skeleton 
differs from the skeleton of an ape. 

Why is it important that the skeleton be kept in proper shape dur¬ 
ing early life ? Mention four ways in which parts of the skeleton may 
be deformed. 

How would you care for a person with a fractured limb? What is 
a dislocation ? a sprain? What is the best treatment for a dislocation 
or a sprain? 

What effect has tobacco on the skeleton? 


Carefully measure your height in the morning. Then measure it 
again at night after you have been moving about all day. Are you 
taller in the morning or in the evening? Why? 

Do you know any animals that have the skeleton on the outside of 
the body? What great advantage is this to these animals? What 
do crabs, lobsters, crayfish, and many insects find it necessary to do 
when the body increases in size? An earthworm has no skeleton. 
How does it cause its body to move in crawling? 



CHAPTER VI 


THE MUSCLES 

The skeleton supports the body. The muscles move it. 
When we think of a living animal, we think of it as having 
the power to move. Yet without muscles we and all the 
animals we see about us would lie quiet, like dead matter. 
It is by the power of the muscles that the giant whale is 
driven through the sea, and the wild bird is carried through 
the air. Muscles cause the wings of the mosquito to vibrate 
faster than the eye can see; they move the creeping snail. 
The muscles carry our feet along, they lift our arms, they 
keep our hearts beating night and day. The pozver by which 
a muscle causes movement lies within its cells- 1 

The Muscles. The skeleton is the framework of the body, 
and the muscles are stretched on the framework, sliding 
smoothly and noiselessly over one another in their move¬ 
ments. They form the chief part of the flesh which rounds 

1 The tissues that we have studied up to this time are the supporting tissues of 
the body, and the pupil should get clearly in mind the difference between them 
and the other tissues. The function of bone, cartilage, and connective tissue is 
to support the body. Since this work is too heavy for soft cells, the cells of sup¬ 
porting tissues become builders and construct a great framework to support the 
body. The bone cells build bone fibers and hard mineral matter. The con¬ 
nective tissue cells build tough connective tissue fibers, and the cartilage cells 
build the groundwork of cartilage. Supporting tissues are composed of cells and 
materials which the cells have built. Other tissues are composed entirely of cells. 
Muscle tissue is composed of muscle cells, the largest and most active cells in 
the body. 


DELTOID 


TRICEPS 

LATISSIMUS 
OORSI 


GLUTEUS 

MAXIMUS 


VASTUS 

LATERALIS 


SEMITENDINOSUS 



PECTORAUS 
MAJOR 


BICEPS 


OBLIQUL'S 

ABDOMINIS 


RECTUS 

ABDOMINIS 


SARTORIUS 


PATELLA 

(BONL) 


TIBIA 

(60NQ 


Fig. 34. The outer muscles of the body. 


60 











































































THE MUSCLES 


6r 


out the body. They number more than five hundred, and 
more than two fifths of the entire body weight is muscle. 
The lean meat of animals is muscle, and by examining the 
body of an animal in a butcher shop, you can see that a 
great portion of the entire body is composed of muscles. 

The Functions of Muscles. The first and chief function of 
the muscles is to move the body. The muscles cause the move¬ 
ments when we walk or run, when we turn the head or eyes, 
when we swallow, when we breathe, or when the heart beats. 
The body cannot move in any way except by means of the 
muscles. 

The second fmiction of the muscles is to help the bones in¬ 
close the body cavities , and thus protect the delicate internal 
organs. 

The third function of the muscles is to assist the ligaments 
in binding the skeleton together at the joints. Nearly every 
muscle in the body stretches across a joint and is attached 
on each side of it, and the strong muscles are a great aid in 
holding the skeleton together. 

How the Muscles move the Body. Muscle cells 1 are so 
long that they are often spoken of as muscle fibers. They 
have the power of contracting, or of drawing up and becoming 
shorter and thicker, as a worm does in crawling. When the 

1 The cells of voluntary and involuntary muscles are very different in appear¬ 
ance. Involuntary muscle cells (Fig. 5) are spindle-shaped, and are several 
times as long as the average body cell. Voluntary muscle cells (Fig. 35) are 
slender fibers often two and a half inches long, which is many hundreds of times 
longer than an ordinary cell (see footnote on page 4). An involuntary muscle 
cell, like an ordinary cell, has only one nucleus. A voluntary muscle cell has 
thousands of nuclei. The reason for this is that the nucleus is the part of the 
protoplasm that enables the cell to take in and use food, and one nucleus would 
not be enough for a cell containing the great amount of protoplasm found in a 
voluntary muscle cell. 


62 


HUMAN PHYSIOLOGY 


BLOOD VESSEL 


cells in a muscle contract, the whole muscle is shortened. 
This causes a bending at the joint over which the muscle 
passes, and a movement of some part of the body, since 
the muscle pulls on the bones to which it is attached. From 
Figure 39 you can understand how, when the biceps muscle 
contracts, the arm is bent at the elbow and the hand raised. 

Voluntary and Involuntary Muscles. Muscles are divided 
into two great classes, — voluntary and involuntary muscles. 
Voluntary muscles are under the control of the will. They are 
governed by the brain, and we can contract them when we 

wish. Try to raise your hand 
and you can do so, because it 
is moved by voluntary muscles. 
Nearly all the voluntary mus¬ 
cles are attached to the skele¬ 
ton. 

Involuntary muscles are not 
under the control of the will. 
They are governed by the sympa¬ 
thetic nervous system, and over 
them the will has no control. If 
food were started down your 
throat, you would be compelled 
to swallow it even though you 
knew it contained poison, for the 
muscles of the throat are invol¬ 
untary muscles. The involun¬ 
tary muscles are found chiefly in 
the blood vessels, walls of the 
heart, digestive organs, and in 
other internal parts of the 
boayT^ 



Fig. 35. A is a portion of a muscle 
showing the connective tissue cover¬ 
ing (perimysium) and the connec¬ 
tive tissue partitions which divide 
the muscles into bundles of muscle 
cells (fasciculi). In B a part of a 
bundle of cells is shown more highly 
magnified. The length of the mus¬ 
cle cells is so great that only a small 
portion of any one cell can be shown. 



THE MUSCLES 


63 


The Connective Tissue Skeleton of Muscles. The muscles 
are held together by connective tissue, and the arrangement of 
this tissue in a voluntary muscle is very 
similar to its arrangement in a nerve. 

A muscle has a connective tissue 
sheath, which covers it like a thin 
skin (Fig. 35). Connective tissue 
partitions 1 run in from the sheath all 
through the muscle, dividing the mus¬ 
cle cells into groups and tying them 
up into bundles. Fine fibers of con¬ 
nective tissue are woven in among the 
individual muscle cells, so that the 
muscle has around it, and running all 
through it, a framework of connective 
tissue. 2 The connective tissue passes 
out at the ends of a muscle and, be- 

1 

coming entangled and interwoven with 
the fibers of the periosteum, attaches 
the muscle to the skeleton (Fig. 36). 

Tendons. The connective tissue may 
pass directly from the muscle into the 
periosteum of the bone. Often, how¬ 
ever, the connective tissue from a mus¬ 
cle unites and forms a tough white 


1 In a piece of meat cut “ across the grain ” ( i.e. 
across the muscle cells) the connective tissue parti¬ 
tions in the muscle may easily be seen. 

2 Not- only the muscles, but the whole body has 
a complete framework of connective tissue. If all 
materials of the body except the connective tissue 
were removed, there would still remain the form 
of the whole with all the organs in place. 



Fig. 36. Diagram show¬ 
ing how the connective tis¬ 
sue passes through a muscle 
from bone to bone. The 
muscle cells are shown 
many times larger than they 
would actually appear. 









6 4 


HUMAN PHYSIOLOGY 


cord called a tendon. The tendon passes to a bone — some¬ 
times to a bone at a considerable distance from the muscle — 
and attaches itself to the bone by spread¬ 
ing out on its surface and sending its 
fibers in among the fibers of the perios¬ 
teum. 

Uses of Tendons. Certain parts of the 
body (the hands, for example) need to 
have great strength and to be capable of 
making a variety of movements, without 
at the same time becoming so covered 
with muscles that they will be large and 
heavy. In such parts of the body, the 
muscles are placed at a distance and 
joined to the bones by tendons. There 
are nearly thirty muscles for moving the 
fingers of each hand. If all these mus¬ 
cles were on the hand, it would not be 
very beautiful, and would be too clumsy 
to do any fine work. The muscles that 
move the fingers are, therefore, placed 
on the forearm, and only slender tendons 
run down to the hand. Open and close 
your hand, and you can see and feel the 
muscles working in your forearm, and in 
the wrist and back of the hand you can 
see the movements of the tendons which 
close and open the fingers. 

Tendons held in Place by Ligaments. 
In Figure 37 you can see that the tendons 
pass under strong ligaments which surround the wrist. In 
many other parts of the body there are ligaments forming 



Fig. 37. The muscles 
of the forearm and the 
tendons and ligaments of 
the hand and wrist. 







THE MUSCLES 


. 65 


bands and loops, which hold the tendons down close to the 
bones. You can learn the necessity for these ligaments by 
an experiment, and the same experiment will teach you 
something about tendons. 


Tie a piece of string about the tip of the first or second finger. 
Run the string back along the front of the finger, across the palm, 
and up the wrist to the forearm. This string is to represent a tendon. 
Now get one of your schoolmates to tie strings around your finger, 
hand, and wrist, as you see in Figure 38. These strings represent the 
ligaments which hold the tendons in place. From up on the fore¬ 
arm pull on the cord which represents the tendon. What effect has 
it on the finger and hand? Cut the cords which represent the 
ligaments, and pull on the cord representing the tendon as before. 
Does the cord follow the curves of the fingers and hand, and lie 
down flat along the bones? What difficulty would we have in the 
hand if the tendons were not tied down to the bones? Now turn 
the string about and run it down the back of the finger and hand, 
and note how a tendon pulling on the back of the finger will open it. 


From this experiment you will understand the use of the 
ligaments in the hand and wrist; you will also realize that 
without the ligaments around the 
ankles, the tendons would rise and 
run straight from the toes to the 
muscles below the knees; and that 
all through the body it is very 
necessary for the tendons to be tied 
down close to the skeleton. 

Constant Contraction of Muscles. 

Lay the back of your hand on the 
desk, stiffen your arm at the elbow, 
and bear down on the desk. Now 

feel the muscle on the back of your Fig. 38. illustrating how a ten- 
y . , 1 j don bends a finger. 

upper arm. It is hard and con¬ 
tracted. It is keeping your arm from bending by pulling on 






66 


HUMAN- PHYSIOLOGY 


the point of the ulna at the elbow. Now stand on one leg 
with the knee of that leg slightly bent, and feel the muscles 
both above and below the knee. They are tightly contracted 
because they are holding the knee and ankle joints from 
giving way under the weight of the body. 

You know that if a man goes to sleep 
when sitting up, his head falls forward. 
The muscles which support the head must 
keep a constant contraction to hold it erect, 
and when the man goes to sleep these 
muscles relax. A dead body will not stand 
up, but will give way at the joints. The 
living body can stand up because the mus¬ 
cles keep the body 
from bending at 
the ankles, knees, 
hips, and in the 
back. Not only 
when the body 
moves, but when 
any part of it is 
held erect or ex¬ 
tended, the mus- 

FIG.39. The antagonistic action of the biceps and , , 

triceps muscles. 111 UbL DC LOn ' 

tracted to hold it 

in position. Try holding the arm extended for five minutes, 
or standing perfectly still for some time, and you will soon 
find that some of your muscles are doing heavy work, al¬ 
though there is no movement of the body. 

Antagonistic Muscles. Many of the muscles of the body 
are in pairs, each muscle of the pair working against the 
other. Muscles which oppose each other in this way are 






THE MUSCLES 


67 


called antagonistic muscles. An excellent example of a pair 
of antagonistic muscles is found in the upper arm. On the 
front is the biceps , which lifts up the forearm. On the back 
of the arm is the triceps , which straightens out the forearm. 
In the leg, both above and below the knee, other antagonistic 
muscles will be found, and as you study the muscles of the 
body, you will note that nearly all of them are arranged 
to work in opposition to other muscles. This is necessary, 
for a muscle cannot push, and if a part of the body is to 
be moved back and forth, it must have a muscle to pull it 
each way. 

Accuracy of Motion given by Antagonistic Muscles. The 

antagonistic action of muscles is very important in giving us 
control of our movements. Suppose you wish to extend the 
forearm to pick up something. You do this by contracting 
the triceps. If there were no biceps, the forearm would be 
thrown out with a jerk, and would probably go beyond the 
object for which you were reaching. But as the muscles are 
arranged, the biceps exerts a steady, even pull against the 
triceps, and when the hand has been extended far enough, 
the biceps gives a pull strong enough to balance the action 
of the triceps, bringing the hand to a stop at just the right 
place to grasp the object. The brakes on a street car or on 
a railroad train make it possible to stop at the desired place. 
In the same way, the antagonistic action of the muscles en¬ 
ables us to check the movements of the body and keep them 
from going too far. 

The Nervous Control of the Muscles. The way in which 
. the nervous system controls all the muscles and makes them 
move the body about, seems almost as wonderful as a story 
from the Arabian Nights. You look at a book and wish to 
read in it; your hand reaches out and grasps the book, opens 


68 


HUMAN PHYSIOLOGY 


it at the place where you wish to read, and holds it up before 
your eyes. You wish to go out of the room; your body 
rises, your feet carry you along, and out of the room you go. 
You wish to throw a ball to one of your playmates; the 
muscles of your legs and back, the muscles which draw back 
the shoulder, arm, and hand, those which draw these parts 
forward again, and the muscles which open the hand to re¬ 
lease the ball, are all brought into action. Each one of this 
great number of muscles must contract at exactly the right 
time, with exactly the right force, and must not remain con¬ 
tracted a moment too long, or the ball will go wide of the 
mark, and you will make a poor throw. 

All such movements are accomplished, not by each muscle 
working independently, but only through the nervous system, 
which controls them all. From the brain or spinal cord a nerve 
goes to every voluntary muscle in the body, and a branch of 
a nerve fiber goes to each muscle cell (Fig. 102). When 
you wish to make a certain movement, the commands pass 
through the nerves to the proper muscles, the muscle cells 
contract, and the movement is made. 

The voluntary muscle cells are controlled by the central 
nervous system. Many commands are sent to them without 
our thinking about it; many movements have been made by us 
so often that the cord and brain send the right commands 
without thought. But all of the voluntary muscles 1 are under 
the control of the will, and when we desire to do so, we can 
send a message from the brain to any one of these muscles 
and make it contract. 


1 The muscles that are used in breathing are in a sense intermediate between 
the voluntary and involuntary muscles. We can control them for a short time; 
but if the breath is held, they soon act in spite of the will. Try holding your 
breath and you will find that it is possible to do so for only a short time. 


THE MUSCLES 


69 


THE CARRIAGE OF THE BODY 

It would be interesting and profitable 1 to locate a number 
of the more prominent muscles of the body and to study their 
action, but we have time 
to take up only the mus¬ 
cles that support the spinal 
column. From your study 
of the skeleton you already 
understand that the entire 
upper part of the body 
stands up on the spinal 
column as on a stem (Fig. 

19), and that if the spinal 
column droops, the head 
and the whole framework 
of the chest must stoop 
forward. It is therefore 
not necessary to explain 
to you why these muscles 
are so important from the 
hygienic standpoint. 

The Long Muscles of the 
Back. Along the dorsal 
side of the spinal column 
are long muscles for supporting the spine and for keeping 
the skull from falling forward. The muscles of the back are 
heaviest in the lumbar region (the “ small of the back ”), 

1 To THE teacher : If time will permit, some exceedingly valuable work may 
be done by having the pupils learn the origin, insertion, and action of some of 
the muscles shown in Figure 34. The most interesting and profitable part of the 
work will be the location of these muscles on the body. 




70 


HUMAN PHYSIOLOGY 


where the two large erectors of the 
spine (erector spinae) may easily be 
felt on either side of the spinous 
processes (Fig. 21) of the vertebrae. 

When the long muscles of the 
back contract they straighten the 



sternomastoid upper part of the spinal column, 


as the tendons on the backs of 


the fingers open the hand. When 


the muscles of the back are weak 
they allow the head and the upper 
part of the spine to droop forward, 
spoiling the appearance and allow¬ 


ing the framework of the chest to 


drop down and crowd the lungs 
and heart. 


The Abdominal Muscles. The 


ERECTOR. 

SPINAE 


.OBUQUUS 

ABDOMINIS 


abdominal muscles are long, thin, 
flat muscles lying in the abdominal 

RECTUS 

abdominis walls. These muscles connect the 
ribs and sternum with the rim of 
the pelvis and prevent the upper 
part of the trunk from being 
drawn over backward by the long 



muscles, and not the muscles of the inal muscles also hold the internal 



shoulders, that hold the body erect, organs in place, and by forcing the 
internal organs back against the dorsal wall of the abdominal 
cavity, support the spinal column in front in the lumbar 
region. 


The Psoas Muscles. The heavy psoas muscles are attached 
along the spinal column in the lumbar region. These muscles 




THE MUSCLES 


have two functions. They lift the thigh, or if the leg is held so 
that it cannot be raised, they bend the body forward at the hips. 
They also brace the spinal column on the froiit of the lumbar 
curve, preventing too great a forward curvature at this point. 

How to acquire and keep an Erect Carriage. In bringing 
the body to an erect position, the great thing is to straighten 
out the curves of the spi¬ 
nal column. Straighten 
the upper curve, and the 
head and chest will be 
lifted. Straighten the 
lower curve, and the ab¬ 
domen will be drawn in. 

Teach the muscles on 
both sides of the spinal 
column to keep the 
proper contraction, and 
the body will stand erect. 

The easiest way of train¬ 
ing the muscles to do this 
work properly is to stand 
and walk as though you 
a little back of the center. This will cause the spinal column 
to be straightened out, pull in the abdomen, and bring up the 
head until it balances on top of the spinal column. Stand in 
this position, and note that your head is back and your chin 
is close to your neck, your ribs and sternum are lifted off the 
heart and lungs, and the muscles are tightened across the 
abdomen, forcing the abdominal organs back and up. “ Stand 
tall,” thrusting up the top of the head as high as possible, and 
drawing the chin and abdomen in, is the best rule for position 
in standing and walking. 



Fig. 42. A diagram of a cross-section through 
the lumbar region of the body. The erectors of 
the spine (erector spinae) and the psoas muscles 
acting against each other keep the spinal column 
erect. 

were hung by the top of the head. 







72 


HUMAN PHYSIOLOGY 


Mistakes made in trying to stand Erect. The most com¬ 
mon of all mistakes made in trying to acquire a good carriage 
is to try to hold the body erect by forcing back the shoulders. 
Contracting the trapezius muscles (Fig. 34) and drawing the 
scapulas back toward the middle of the back, or pulling the 
shoulders back with braces, will never bring the body to an 
erect position. 1 The true remedy is to straighten out the 
spinal column. The shoulders will take care of themselves if 
only a little care is used to see that they are not lifted too 
high when the body is straightened up. 

The other common mistake made in trying to stand erect 
is to throw the head and chest up and allow the abdomen to 
be thrust forward. The trouble is that although the muscles 
along the back are contracted, bringing up the upper part of 
the spine, yet the psoas and abdominal muscles are allowed 
to relax, and the spinal column bends inward in the lumbar 
region. 

Importance of acquiring a Correct Carriage in Youth. If 

the body is not held erect in youth the bones will harden in a 
stooping position, the cartilages between the vertebrae will 
become wedge-shaped, and the muscles will develop in length 
to fit a stooped skeleton instead of a straight one. Youth 
is also the best time to build up and strengthen weak mus¬ 
cles, and to teach all the muscles to keep a proper amount of 
contraction. 

The easiest way to acquire an upright carriage is to form 
the habit of sitting, standing, and walking erect. “ Stand 
tall,” and the muscles will fall into the habit of keeping the 
spinal column upright. It is possible, however, by suitable 

141 The position of the shoulders has hardly any effect upon the position of the 
body. They hang upon the outside of the body like the blinds on a house.” 
— Dr. Luther H. Gulick. 


THE MUSCLES 


73 


exercise, to develop and strengthen weak muscles, and if you 
are inclined to stoop you should exercise especially the mus¬ 
cles that support the spine. 

HYGIENE OF MUSCLES 

All the cells of the body live together, and it is not possible 
to have some of them in bad condition and the remainder of 
them in good health. Whatever keeps the whole body in 
health, therefore, benefits the muscles. Among these things 
are plenty of good food, fresh air, and sleep. Other things 
that are necessary, not only for the health of the muscles but 
for the health of the whole body, are exercise and rest. 

Importance of Exercise. Exercise benefits the body in 
many ways. It quickens the breathing and starts the heart 
to beating faster, and it stirs up the different organs of the 
body and causes more blood to flow through them. Without 
exercise the muscles become weak and soft, and it is also true 
that if the muscles are not exercised the whole body, espe¬ 
cially the digestive organs, will get out of order. A whole 
book could be written on this subject, but any one who 
wishes to take healthful exercise knows how to do so, and 
we will merely call your attention to the following important 
facts: 

The muscles should be exercised every day. Any one who 
is lazy and neglects to do this will surely suffer, for without 
exercise the body cannot keep in health. Exercise should be 
stopped before one becomes too tired , for too much exercise is 
worse than not enough. Whenever possible , exercise should be 
taken outdoors. Outdoor games furnish enjoyment, fresh air, 
and exercise all at the same time and are the best of all forms 
of exercise. 


74 


HUMAN PHYSIOLOGY 


• Effects of Tobacco and Alcohol on the Muscles. Tobacco, 
so far as we know, is injurious to all of the body cells. 
Certainly it weakens the muscles. Athletes who wish to have 
their muscles in such condition that they will contract with the 
greatest possible power, are not allowed to use tobacco. 

Alcohol also weakens the muscles, especially in any long- 
continued effort. Shrewd old Benjamin Franklin knew this 
long ago. In speaking of the time when he worked in a 
London printing house, he says : “ I drank only water. The 
other workmen, fifteen in number, were great drinkers of beer. 
On occasions I carried up and down stairs a large form of 
types in each hand, when others carried but one in both 
hands. They wondered to see from this and several in¬ 
stances, that the Water-American, as they called me, was 
stronger than themselves, who drank strong beer.” 

Arctic explorers have found that they fared best when they 
used no alcohol. In mountain climbing, in the cold air of the 
high Alps, it has been found by experiment that a man could 
do 20 per cent more work on days when he used no alco¬ 
hol than the same man could do on days when a moderate 
amount of alcohol was used. In the hot climates of Africa 
and India it has been found that regiments of soldiers with¬ 
out alcohol can outmarch those using it. Thus in both cold 
and heat, alcohol users have less endurance than those who 
do not use it. Both alcohol and tobacco weaken the muscles, 
and they do this chiefly by injuring the nervous system, 
which controls the muscles. 

Summary. The muscles number more than five hundred 
and make up more than two fifths of the body weight. They 
move the body, help inclose the body cavities, and assist in 
binding the skeleton together. The two glasses of muscles 
are the voluntary and involuntary. 


THE MUSCLES 


7 5 


A muscle has a framework of connective tissue by which 
it is attached to the skeleton. In some cases the connective 
tissue forms a tendon and runs to a bone at a distance from 
the muscle. The tendons are held down close to the skele¬ 
ton by ligaments. 

The muscles of the body keep a certain amount of contrac¬ 
tion, as is shown by the fact that a dead body will not stand 
up. Most of the muscles are arranged in pairs, one muscle 
of the pair working in opposition to the other. The nervous 
system controls the muscles and causes them to work together 
in a wonderful manner. 

In the carriage of the body, the muscles of the spinal 
column are the ones that are important. The erectors of the 
spine, the abdominal muscles, and the psoas muscles support 
the spinal column and should be taught to keep a proper 
amount of contraction. The best way to do this is to form 
the habit of standing and walking erect. 

A common mistake in trying to acquire an erect carriage 
is to pull the shoulders back instead of straightening up the 
spinal column. Another mistake is to allow the spinal column 
to bend forward too much in the lumbar region. In youth 
is the time to acquire a good carriage. 

Exercise is necessary, not only for the health of the mus¬ 
cles, but for the health of the other organs of the body as 
well. Tobacco and alcohol weaken the muscles and should 
not be used by those who wish to be strong. 

QUESTIONS 

How manv muscles are in the body? How much of the body 
weight is muscle? 

Give three functions of the muscles. What causes a muscle to 
contract? Explain how the biceps muscle bends the arm. Name 


76 


HUMAN PHYSIOLOGY 


the two classes of muscles. What is the difference between them? 
To what are the voluntary muscles attached? Where are the invol¬ 
untary muscles found ? 

Describe the connective tissue skeleton of a muscle. How is a 
muscle attached to a bone? Of what is a tendon composed? What 
advantage is there in having tendons in the body? How are the 
tendons kept close to the bones? 

Why does a man’s head remain erect when he is awake and fall 
forward when he goes to sleep? What are antagonistic muscles? 
Give an example. Why are the muscles of the body arranged in 
pairs? What effect have the antagonistic muscles on our movements ? 

What has the nervous system to do with our movements? By 
what part of the nervous system are the voluntary muscles controlled? 
Where are some of the muscles that are used in walking? Do you 
think of the movements caused by all these muscles? 

What part of the skeleton supports the head and trunk? What 
muscles keep the upper part of the spinal column erect? What fol¬ 
lows if these muscles are weak or relaxed too much? Give two 
functions of the abdominal muscles; two functions of the psoas 
muscles. If these muscles are weak or relaxed, what effect has it on 
the curves of the spinal column? What is the best method of train¬ 
ing the muscles to hold the spinal column erect? Give the rule for 
position in standing and walking. What two mistakes are often made 
in trying to stand erect? Why is it important to acquire a correct 
carriage in youth ? 

Name four things necessary to the health of the body. Mention 
some of the effects of exercise on the body. What effect has lack of 
exercise on the muscles? on the other organs of the body? What 
three important statements are made in regard to exercise? 

What effect has tobacco on the muscles? Tell of Franklin’s expe¬ 
rience in the London printing house. What effect had alcohol on the 
power of a man to work in the cold air of the Alps Mountains ? What 
effect has it on the endurance of men in hot climates? In what way 
do alcohol and tobacco chiefly affect the muscles? 


THE MUSCLES 


77 


REVIEW QUESTIONS 

Chapter I. Of what are living things composed? How do cells 
originate ? Why is it necessary that there should be a division of 
labor among the cells of the body? Name some of the different 
kinds of cells in the body and give their functions. 

Define : protoplasm; nucleus; tissue; organ; anatomy ; physi¬ 
ology; hygiene. 

Chapter II. Name and locate the two body cavities. What is in 
each? Where does man belong in the animal kingdom? Mention 
some ways in which the bodies of all vertebrates are alike. How 
does the human body differ from the bodies of all other animals? 

Chapter III. What is the function of the nervous system ? Explain 
why some such system is necessary in the body. Name the divisions 
of the brain. Describe a nerve. What is the function of the nerves? 

Define and give the function of the following: central nervous 
system; sympathetic; dura mater; arachnoid; pia mater; cerebro¬ 
spinal fluid. 

Chapter IV. Give three functions of the skeleton. What part of 
the skeleton forms a central axis to which all the other parts are 
joined? Name bones of different shapes with their functions. What 
materials are in bones, and what is the function of each kind of 
material? What advantage is there in the hollow structure of bones? 

Define : compact; spongy; marrow; periosteum. 

Chapter V. Name two classes of joints; three kinds of movable 
joints. Describe cartilage and tell where it is found. How is 
friction kept down in the joints? What are ligaments? How is 
the skeleton made springy? How does the human skeleton resemble 
other vertebrate skeletons? How does it differ from the skeleton of 
an ape? Mention some points in connection with the hygiene of 
the human skeleton. How would you treat a broken bone? a 
dislocation ? a sprain ? 

Chapter VI. Give the functions of the muscles. How are muscles 
attached to bones? Explain how the muscles move the body. What 
muscles are important in the carriage of the body? How may an 
erect carriage be acquired? What mistakes are made in trying to 
stand erect ? Why should the body be carried erect in youth? Speak 
of the importance of exercising the muscles; of the effects of tobacco 
on the muscles; of the effects of alcohol on the muscles. 


CHAPTER VII 


FOODS AND ENERGY 

To-day we take in food. To-morrow the food is gone and 
we are hungry still. We eat again and the next day find our 
need for food as great as it was at first. We spend our lives 
working for food and eating food, and yet only a few short 
hours behind, hunger is always following on our trail. 

Why can we not forget all about food ? What makes us 
want to eat ? Why do we spend our money for something 
that we cannot keep ? Why not give up eating and have time 
to rest and enjoy life? Because zvithout food the life of the 
cells and of the body comes to an end. 

Why the Cells need Food. The living protoplasm in the 
cells is continually wasting away. In certain parts of the 
body the cells are constantly dying 1 and being replaced by 
new cells. Other new cells are needed when the body grows 
in size (page io). New protoplasm, therefore, is constantly 
being built up for the repair and growth of the cells, and 
this protoplasm is formed from the materials that are in the 
foods. Food is necessary to furnish material for the repair 
and grozvth of the cells. 

The cells get their energy — their warmth and power to 
work — from the food. A muscle cell gets its strength, a 

1 It is estimated that fourteen billion red blood corpuscles die in the body every 
day. Great numbers of cells also die on the surface of the skin. 

78 


FOODS AND ENERGY 


79 


bone cell gets its power to build bone, and all other cells, 
whatever they do, get their power to work from the energy 
which is in the food. Just as a locomotive gets its energy — 
its warmth and power to move—from the fuel which is burned 
under its boiler, so the cell gets its energy from the food 
which is burned within the cell. Cut off the fuel from a 
locomotive, and it will became cold and still. Cut off the 
food from a cell, and it will lose its energy and become a dead 
cell. Food is necessary to furnish energy to the cells. 


THE CHEMISTRY OF FOODS 

Molecules and Atoms. In the study of chemistry we learn 
that everything that we can see, feel, taste, or smell is com¬ 
posed of very small parts called molecules. Just as a house 
is built of bricks, so are wood, stone, water, earth, air, and 
other substances composed of molecules. 

Molecules are so small that millions of them are required 
to build the smallest object that can be seen with the most 
powerful microscope. They are so small that we cannot 
imagine how small they are. Yet chemists study molecules, 
and they have discovered some very wonderful things about 
them. One of the most wonderful of these discoveries is 
that molecules are composed of still smaller particles called 
atoms. There are about eighty kinds of atoms, all differing 
in many ways. 

Elements and Compounds. Elements are substances that 
have only one kind of atoms in their molecules. Compounds 
have two or more different kinds of atoms in their molecules. 
Perhaps you do not understand what you have just read, but 
if we play that we are building molecules, you will probably 


8o 


HUMAN PHYSIOLOGY 


get a clear idea of the difference between an element and 
a compound. 

Suppose we have a pile of bricks of many different colors, 
— some purple, some red, some yellow, some green, some 
blue, and some violet. Suppose we call these bricks atoms, 
and of them decide to build molecules. Let us first build 
a molecule using only red bricks. This is like the molecule 
of an element, for it has only one kind of atoms in it. Let us 
now build a molecule of yellow bricks. This also is like the 
molecule of an element, for only one kind of atoms was used 
in making it. Now let us build a molecule partly of yellow 
and partly of red bricks. Is this like the molecule of an 
element? No, for it has in it two kinds of atoms. It is like 
the molecule of a compound. Let us now build a big mole¬ 
cule and put into it all the different kinds of bricks that 
we have. Is this big molecule an element or a compound ? 
Read the definition of a compound again, and you will see 
that this is- certainly a compound. 

Some Common Elements and Compounds. Since there are 
eighty kinds of atoms, there are about eighty elements. You 
could tell that iron is an element from 
the diagram of its molecule, for both 
atoms are of the same kind. Gold is 
another element, the atoms in its mole- 
Other common 



FIG. 43. A molecule of iron. 

Iron is an element because all Cllle being the Same. 


the atoms in its molecule are elements are silver, copper, lead, tin, 
of the same kind. . 

zi?ic f sulfur , and carbon (the black sub¬ 
stance of which charcoal and soot are composed, and which 
you see on the burnt end of a match). Still other elements are 
oxygen , the gas which is taken into the blood from the air when 
we breathe; hydrogen , a very light gas used to fill balloons; 
and nitrogen , a gas making up about four fifths of the air. 



FOODS AND ENERGY 


8l 



Since the eighty different kinds of elements combine in 
very many different ways, there are thousands of compounds 
all about us. Wood, stone, water, 
and earth are all compounds. 

Rocks and the ores of metals are 
compounds. Dynamite and gun- 

, Fig. 44. A molecule of water, 

powder are compounds whose Water is a compound because it has 
molecules fly to pieces with great more than one kind of atoms in its 
force. Everything that,you eat molecule - 
and wear is a compound, and if you should pick up the thing 
nearest your hand, you would probably find that you were 
holding a compound. 

Compounds Different from the Elements of which they are 
formed. When blue and yellow paint are stirred together, 
the mixture is neither blue nor yellow, but green. So a com¬ 
pound may be very different from any of the elements of 
which it is formed. Thus when carbon (a black solid) and 
sulfur (a yellow solid) unite, they make a liquid. When oxy¬ 
gen and iron unite, they make the red rust which you have 
so often seen. This rust is not a gas like oxygen, nor is it a 
tough and hard metal like iron. It is a compound, and very 
different from each of the elements (oxygen and iron) of 
which it is made. 

Water is another compound which is different from either 

of the elements in it. Hydrogen 

and oxygen are both gases, but 

when they unite, they form water, 

a liquid. Carbon and oxygen also 

dioxid. This gas is a compound,its form a compound very unlike 

molecules having in them two kinds either of the elements entering 
of atoms. 0 

into it. A piece of charcoal is 
a black solid which you can see and handle, and oxygen is 


/ OXYGEN \ >/CARBONlV / OXYGEN \ 
l ATOM ATOM ATOM I 

Fig. 45. A molecule of carbon 






82 


HUMAN PHYSIOLOGY 


the gas of the air which is so necessary to our lives. But 
when carbon and oxygen unite (as they do when you burn a 
piece of charcoal) the compound, carbon dioxid, is a poisonous 
gas very different from the solid carbon, and also very 
different from the life-supporting oxygen. 

The Language of Chemists. Chemists do not write out the 
whole names of the elements, but write H for hydrogen, O 
for oxygen, S for sulfur, C for carbon, and other short signs 
for the other elements. They have also a short way of writ¬ 
ing out the kinds of atoms and how many of each kind are in 
a compound. Thus they write H 2 0 (read: H two O) for 
water, meaning that in a molecule of water there are two 
atoms of hydrogen and one atom of oxygen. For carbon 
dioxid, the poisonous gas which we breathe'out from the 
lungs, and which is formed when anything containing carbon 
is burned, they write C 0 2 (read: CO two), meaning that in a 
molecule of this gas there are one atom of carbon and two of 
oxygen. 


CLASSES OF FOOD 

From plants and animals the people of the world obtain 
many different foods. All these foods, however, can be put 
into three great classes, — the carbohydrates, fats, and proteids. 

Carbohydrates. The carbohydrates include the starches 
and sugars. Almost all of them come from plants. Nearly 
every plant has its own kind of starch, and we have corn 
starch, wheat starch, oat starch, potato starch, arrowroot 
starch, and many other varieties of starch. All the grains, 
potatoes, and most vegetables are starchy foods. 

Sugar is an important food. Most of the sugar that we 
use comes from sugar cane and the sugar beet. Besides what 


FOODS AND ENERGY 


83 


we purposely add to our foods to make them pleasant to the 
taste, we get considerable amounts of sugar in maple syrup, 
molasses, honey, and fruits, and there is some sugar in corn, 
sweet potatoes, milk, and many other foods. 

Fats. There is no difference between fats and oils, except 
that at ordinary temperatures fats are solid and oils are 
liquid. For use as food they are the same, and are all called 
fatty foods. 

Among the common fatty foods are butter, taken from 
milk; lard and cotton-seed oil, used in cooking; olive oil, used 
in salads and dressings; and the fat that is always found in 
meat. Besides the fats obtained from these foods we get 
some fats in eggs, cheese, corn, chocolate, and in a great 
many other foods. 

Proteids. Most of the food that we get from animals con¬ 
tains proteids. Lean meat, fish, eggs, milk, and cheese, all 
contain proteid matter. Corn and all the cereal grains except 
rice contain considerable proteid matter; but of all common 
foods obtained from plants, peas and beans are the richest in 
proteids. The table in the back of the book shows the pro¬ 
portion of proteids, carbohydrates, and fats in many foods. 

Chemical Composition of the Different Classes of Foods. 
The carbohydrates contain the three elements, carbon, 
hydrogen, and oxygen, — and in the common carbohydrates, 
as in water, there are always twice as many atoms of hydro¬ 
gen as there are atoms of oxygen. Thus, common sugar is 
C12H22O1U there being two atoms of hydrogen for one of oxy¬ 
gen. Fats contain the same elements as the starches and 
sugars, but in different proportions, having in them much 
less oxygen than is found in the carbohydrates. Proteids 
contain all the elements (carbon, hydrogen, and oxygen) 
which are found in the other foods, and in addition they 


8 4 


HUMAN PHYSIOLOGY 


contain nitrogen and usually very small amounts of sulfur, 
phosphorus, iron, and other elements. 

All Foods come from Living Things. From what you have 
already learned you will know that the principal elements in 
food are very abundant in the world. Oxygen and nitrogen 
make up nearly all of the air. Water is two thirds hydrogen, 
as you could tell by counting the number and kinds of atoms 
in its molecules. Carbon is abundant in wood; coal is nearly 
all carbon; and there is much carbon in the rocks of the 
earth. 

But you could not live on water, coal, and air. They con¬ 
tain all the chief elements of our food, but it is only when 
these elements have been built up into the proper compounds 
that they are useful in nourishing the body: These com¬ 
pounds we find only in the bodies of living things, so all our 
food must come from the bodies of animals or from plants. 
“ In building our house, we can use only bricks ripped 
from the walls of other houses.” 

Uses of the Different Classes of Foods. Protoplasm is living 
proteid matter; it is always partially composed of nitrogen, 
and any food which is used in cell building must contain 
nitrogen. The proteids are therefore the building foods. 
The fats and carbohydrates lack the necessary nitrogen, and 
cannot be used in cell building. They are fuel foods , useful 
for burning in the cells to furnish energy. The proteids when 
burned also furnish energy to the cells, but their main use 
is to provide materials for building 7 iew protoplasm. 

OTHER THINGS NECESSARY TO THE BODY 

Oxygen and Water. Besides the three classes of foods that 
we have studied, there are certain other substances which the 


FOODS AND ENERGY 


$5 


body must have to keep it in health. Among these things 
oxygen takes the first place. We breathe it in constantly, 
and if the supply of oxygen is cut off for even a short time, 
we die. Water is also absolutely necessary to the body. 
Besides the water that we drink, we get a great deal of water 
in our foods, as you can see by referring to the table of foods 
in the back of the book. Potatoes are more than 80 per 
cent water; beef is more than half water; and even in dry 
foods like rice and beans there is water. 

Minerals. Several minerals are needed by the body. Of 
these salt is needed in the greatest quantity. During the 
time of growth the body must have also a considerable quantity 
of lime to build the skeleton. Iron in small amounts is 
necessary for the formation of the red blood corpuscles, and 
small amounts of several other minerals are needed by the 
body. Some of these minerals we get in water, and others in 
our food. The green parts of vegetables have a special value 
because of the iron they furnish to the red corpuscles of the 
blood. 

Summary. The human body constantly requires food. 
This food is necessary to furnish building material and 
energy to the cells. 

All matter is composed of molecules that are built of still 
smaller particles called atoms. Elements have only one kind 
of atoms in their molecules. Compounds have two or more 
kinds of atoms in their molecules. There are about eighty 
elements and thousands of compounds. Compounds are 
often very different from any of the elements of which they 
are formed. 

The three classes of foods are the carbohydrates (starches 
and sugars), the fats, and the proteids. The carbohydrates 
are obtained chiefly from plants. They contain carbon. 


86 


HUMAN PHYSIOLOGY 


hydrogen, and oxygen, there being in them two atoms of 
hydrogen for each atom of oxygen. Fats and oils contain 
these same elements but in different proportions. Proteids, 
in addition to the elements found in the other foods, contain 
nitrogen. Lean meats, eggs, milk and cheese, grains, and 
peas and beans are the principal proteid foods. 

The elements found in foods are very abundant in the 
world, but only compounds built up by living plants and 
animals can be used by man for food. The proteids give 
energy to the body, and they are the only foods that can be 
used in building protoplasm, because only the proteids con¬ 
tain nitrogen. The other foods furnish energy to the body. 

Oxygen, water, and certain minerals are also necessary to 
the body. The body obtains its minerals from water and 
foods. Green vegetables are especially valuable for their 
iron. 

QUESTIONS 

Give two reasons why the body needs food. Why do the cells 
need building material? Why do they need energy? 

Of what is all matter composed? Of what are molecules com¬ 
posed? What is an element? What is a compound? Name some 
elements; some compounds. Name some compounds that are 
different from the elements of which they are composed. Give 
some examples of the short signs that chemists use. 

What are the three classes of foods? What two kinds of carbo¬ 
hydrates are there? From what are they obtained? Mention some 
starchy foods; some foods that contain sugar. What is the differ¬ 
ence between a fat and an oil ? Mention some fatty foods. Mention 
a number of foods that are rich in proteids. 

What elements are in carbohydrates? In what proportion are the 
hydrogen and oxygen in them ? What elements are in fats ? Give 


FOODS AND ENERGY 


87 


two uses of the proteids in the body. How are the carbohydrates 
and fats used in the body? From what kind of objects are our foods 
obtained? 

Mention some other things that are needed by the body. Where 
does the body obtain its oxygen? water? mineral matter? What 
mineral is especially found in the green parts of vegetables ? 


When gas or oil is burned, what becomes of the atoms of which 
its molecules were composed ? 



CHAPTER VIII 


THE DIGESTIVE ORGANS 


We have now learned that the cells of our bodies must 
have food. But before one of the cells in the brain, for 

instance, can use the 
beefsteak or the potato 
that lies on your plate, 
many changes must be 
made in these foods. 
We therefore have a 
great system of organs 
whose business it is to 
work over and prepare 
the foods for the cells. 
These are the digestive 
organs . Of all parts 
of the body, it is the 
most important to un¬ 
derstand the digestive 
system, for oftener 
than any other part of 
the body, these organs 
fail in their work, and 
interfere with the 
health. 

The Digestive Sys¬ 



VERMIFORM API 


Fig. 46. The digestive organs. 


tem. The digestive system includes the alimentary canal and 

88 












THE DIGESTIVE ORGANS 


89 


certain accessory or assisting organs of digestion, — the teeth, 
salivary glands (Fig. 54), liver , and pancreas. The alimen¬ 
tary canal is a long passageway through the body, into which 
the food is taken while it is being digested. The teeth grind 
the food into small pieces, and the other accessory organs of 
digestion pour juices into the alimentary canal that assist in 
digesting the food. Before beginning the study of the diges¬ 
tive organs it is well to have a general idea of the structure 
and function of a gland, for 
the whole digestive system is 
in the main a collection of 
glands. 

A Simple Gland. In a simple 
gland the cells are arranged 
in the form of a hollow tube 
(Fig. 47). On one side the 
gland cells take in water and 
other materials from the blood. 

On the other side the gland 
cells give off a liquid into the 
hollow in the center of the 
gland. When the gland cells 
give off liquid 1 the liquid 
flows out of the mouth 
of the gland. The gland is then said to secrete , and the 
liquid from a gland is called the secretion of the gland. 

1 In some glands the cells merely take up on one side materials from the 
blood, and on the other side give off the same materials into the central opening 
of the gland. A sweat gland is an example of this class of glands. The water 
and the salt of the perspiration merely flow from the blood through the cells of 
the gland, and come out on the skin as sweat. Other glands build up new sub¬ 
stances with the materials which they take from the blood. The glands of the 



ARTERV 


FIG. 47. A section through a simple 
gland. 






go 


HUMAN PHYSIOLOGY 


THE ALIMENTARY CANAL 

The alimentary canal is almost thirty feet in length. Its 
principal divisions are the mouthy pharynx (throat), esophagus , 
stomachy and the small and large intestine . In its walls are 
muscles that contract on the food and force it onward through 
the canal. Beginning with the lips, the alimentary canal 



Fig. 48. The stomach, liver, and pancreas. 


is lined throughout with a smooth mucous membrane . This 
differs from skin in having a pink color and in being kept 
moist with sticky mucus (Fig. 6), which causes the food to 
move easily along in its course through the alimentary canal. 

The Stomach. The food is taken into the mouth, passes 
back through the pharynx, and goes down the esophagus. 

Stomach are examples of this kind of glands. The cells in these glands build up 
and give forth in their secretion a substance called pepsin y which digests the 
proteid foods. 





THE DIGESTIVE ORGANS 


9 * 


At the bottom of the esophagus is the stomach. This holds 
about three pints, and when full is about a foot long and four 
inches through in the thickest part. When empty, however, 
the stomach draws up and occupies much less space. The 
function of the stomach is to serve as a storehouse for food so 
that enough can be eaten at one time to supply the body for 
several hours, and also to secrete gastric juice. 

The Glands of the Stomach. In the inner coat of the 
stomach wall are great numbers of gastric glands , which 



Fig. 49. A section of the wall of the stomach, showing muscles and glands. B is 
one of the glands more highly magnified. 


secrete gastric juice for digesting the food and for killing 
bacteria. Each gland is a little circular depression (like 
a little well) in the wall of the stomach. If a handkerchief 
be spread over the hand and thrust down into the hand 































92 


HUMAN PHYSIOLOGY 



Fig. 50. To illustrate how 
a gastric gland is formed by 
an infolding of the stomach 
wall. 


with a pencil as you see in Figure 50, the shape of a simple 
gastric gland, and the way it lies in the stomach wall, will be 
very well represented. Some of the 
gastric glands branch in their lower 
parts; but they are all formed by 
folding the inner layer of the stomach 
wall into deep narrow pockets. 
Figure 49 shows how closely these 
glands are packed together, and it 
also shows how small they must be, 
for they do not reach more than 
halfway through the stomach wall, 
although the wall itself is little 
thicker than a piece of heavy cloth. 
The Gastric Juice. From two and a 
half to five quarts of gastric juice are secreted in a day. 
Most of the gastric juice is water, but it contains pepsin for 
digesting the proteid food, and acid. The acid kills many 
bacteria, thus keeping them from getting into the intestine 
and causing trouble there. It is useful in digestion also, since 
without the acid the pepsin is unable to digest the proteid 
foods. 

The Muscles of the Stomach. The entire alimentary canal 
from the top of the esophagus onward, has a circular and a 
longitudinal layer of muscles in its walls. The stomach has 
these two muscle layers, and has in addition a layer of oblique 
muscles. There are, therefore, circular muscles running 
around the stomach, longitudinal muscles running lengthwise 
of the stomach, and oblique muscles running slantingly in the*, 
stomach walls. These muscles force the food onward through 
the stomach; and during digestion, especially in the lower part 
of the stomach, the muscles keep contracting and mixing up 


THE DIGESTIVE ORGANS 


93 


the food in the gastric juice. At the pylorus , or point where 
the stomach joins the small intestine, the circular muscles are 
thickened into a strong ring, the pyloric muscle , which closes 
the opening between the stomach and intestine while diges¬ 
tion is going on in the stomach. After stomach digestion 
has been finished, the circular muscles contract above the 
food, the pyloric muscle opens at the same time, and the food 
is forced into the intestine (page 112). 

The Small Intestine. The small intestine is coiled in the 
abdominal cavity. It is much the longest part of the alimen¬ 
tary canal, having a length 
of nearly twenty-two feet. 

In its walls are intestinal 
glands , very similar to the 
glands of the stomach. 

They secrete the intestinal 
juice , which aids in digest¬ 
ing the food. The juices 
of the liver and of the 
pancreas are also emptied 
into the small intestine, and 
the digestion carried on 
here is even more impor¬ 
tant than the digestion in 
the stomach. 1 

The Villi. 



INTESTINAL GLAND' 


FIG. 51. Villi and intestinal glands. 

On the intestinal wall are many little finger¬ 
like projections called villi (singular, villus ), which stand up 
in the digested food and absorb it, or take it into the body 
through the intestinal wall. So abundant are the villi that 


1 In a few cases the stomach has been removed and the esophagus connected with the 
small intestine. Persons on whom this operation has been performed have lived, the 
digestive work of the stomach being done by the small intestine. 












94 


HUMAN PHYSIOLOGY 


they give the inner surface of the intestinal wall an appear¬ 
ance like velvet, and they absorb the food much more 
rapidly 1 than a smooth, even wall could do. Digestion is 
finished in the small intestine, and most of the liquids and 
the digested food are absorbed before the large intestine is 
reached. A little food, however, passes into the large intes¬ 
tine and is there absorbed while the muscles in the walls of 
the large intestine move onward the indigestible material. 

The Large Intestine. The large intestine, begins low 
down in the right side of the abdominal cavity, passes up the 
right side, then across under the diaphragm, and down the left 
side. Just below where the small intestine opens into it there 
is a small, worm-like structure (Fig. 46), the vermiform 
appendix . 2 The large intestine has no villi. Its glands 
secrete mucus and also throw off into the intestine some 
waste products from the body. 

THE ACCESSORY ORGANS OF DIGESTION 

The Teeth. A tooth is composed of a crown, a neck, and 
one or more roots. The roots stand in sockets in the jaw¬ 
bones, and are covered by a layer of bone-like cement. 
The outer coat of the crown is made of enamel , the hardest 
material in the body. Under the enamel and forming the 
main bulk of the tooth is the dentine , 3 a substance harder 
than the most compact bone, but not nearly so hard as 


1 The villi give from four to eight times as much absorbing surface as the 
smooth walls of the intestine would give. 

2 The disease called appendicitis is caused by germs growing in the vermiform 
appendix and causing inflammation. In severe cases of appendicitis, it may be 
necessary to open the abdominal cavity and remove the vermiform appendix. 

3 Ivory is dentine, usually obtained from the tusks of elephants, but sometimes 
from the tusks of the walrus or the teeth of the hippopotamus. 


THE DIGESTIVE ORGANS 


95 



enamel. In the middle of the tooth is the pulp cavity , a little 
chamber containing nerves and blood vessels. Get a tooth 
from a dentist, or find the tooth of an animal, and break it 
open, and you will have no difficulty in finding the enamel, 
the dentine, the pulp cavity, and 
the little root canals through 
which the nerves and blood 
vessels come up from the jaw¬ 
bone into the tooth. 

Different Kinds of Teeth and 
their Functions. There are four 
kinds of teeth, — incisors, canines 
or cuspids , bicuspids , and molars . 

The incisors are flat and sharp 
for biting off food. In the dog 
and other flesh-eating animals 
the canines are tusks which are 
used as weapons and in tearing 

flesh, but in man their principal use is to assist the incisors in 
biting. The bicuspids and the molars have wide surfaces for 
grinding the food into small pieces and mixing it thoroughly 
with the saliva. Examine a back tooth and notice the cusps , 
or points, on it. Observe how the cusps of the upper and 
lower teeth fit into each other when the jaws are tightly 
closed. Then notice how the jaws move sidewise in chewing, 
and you will readily understand how the food is crushed and 
ground to pieces as the teeth slide across each other. 

Temporary and Permanent Teeth. The jaws in childhood 
are too small to hold the large teeth which we need in later life. 
In early life we have therefore a set of twenty small tempo¬ 
rary teeth, and in later life a set of thirty-two larger permanent 
teeth. The earliest permanent teeth to appear are the first 


Fig. 52. Section of a tooth. 



96 


HUMAN PHYSIOLOGY 


molars, 1 which come in behind the temporary molars about 
the sixth or seventh year. 

Care of the Teeth. Decay of the teeth is caused by bacteria, 
which find a splendid place to grow in the moist, warm food 
between the teeth. It is also thought that bacteria are the 


molars bicuspids canines incisors 



Fig. 53. One half of the permanent teeth. 


cause of tartar, a dark hard substance that collects on the 
teeth of some persons. It is evident that the best way to 
preserve the teeth and to keep them white and beautiful is 
to keep them clean, so that bacteria will find no- food 
materials among them. They should be brushed with pure 
soap or a good tooth powder after each meal, or at least in 
the morning and at night before going to bed. Particles of 
food should be removed from between the teeth with a wooden 
or quill toothpick, or with a piece of thread. It is very 

1 A common error is to mistake the first permanent molars for temporary teeth, 
and to allow them to decay, thinking that they will be replaced by new teeth. 
When there are three double teeth on one side of the jaw, the back one is a 
permanent tooth. 











THE DIGESTIVE ORGANS 


97 


important not to break the enamel by biting on thread, nuts, 
or other hard substances; for where the enamel is broken and 
the dentine exposed, decay soon follows. Tartar should be 
removed by a dentist, for it causes the gums to shrink and 
expose the necks of the teeth below the enamel. 

When decay has begun in a tooth, the only remedy is to 
have the cavity filled by a dentist. This should be done 
before the cavity becomes large and gets down close to the 
nerves in the pulp cavity of the tooth. The teeth are so 
valuable that we cannot afford to lose them, and it is far 
better to have a dentist look them over occasionally and fill 
all small cavities than it is to suffer later from toothache, 
neuralgia, and indigestion, and to pay for crowns, bridge 
work, or artificial teeth. 

The Salivary Glands. There are six salivary glands,—three 
pairs. The two sublingual glands are under the tongue, the 
submaxillary glands are under 
and behind the corners of the 
lower jaws, and the parotid 1 
glands are in front of the ears. 

The saliva is carried from the 
glands to the mouth through 
circular canals called ducts. 

The ducts of the submaxillary 
and of the sublingual glands of 
each side of the head unite 
before they enter the mouth. 

The ducts from the parotid 
gland Open On the inside of FlG - 54 - The salivary glands. 

the cheeks opposite the second molars of the upper jaw. The 

1 In mumps the parotid glands are swollen and inflamed. The other salivary 
glands also are occasionally affected. 



98 


HUMAN PHYSIOLOGY 


saliva is secreted by the cells in the 
small branches of the gland (Fig. 55) 
and flows into the main duct and on 
into the mouth. 

Uses of the Saliva. The saliva 
moistens food and makes it possible 
to swallow dry food like crackers, 
which without saliva would become 
dust in the mouth. The saliva is 
useful also because it contains a 
substance called ptyalin , which di¬ 
gests starch. 

The Pancreas. The pancreas (Fig. 
48) is a long gland, shaped something 
like the tongue of a dog. The Ger¬ 
mans call the pancreas the “ abdomi¬ 
nal salivary gland,” and this is a very 
good name for it, for it is composed 
of many little branches, like a great 
salivary gland, and the pancreatic 
juice is very much like thin, watery 
saliva. The pancreas is the most 
important of all the digestive glands, 
for the pancreatic juice contains 
trypsin , a substance which digests 
proteids, amylopsin for digesting 
starches, and steapsin for digesting 
fats. The pancreatic juice digests 
all three classes of foods very 
rapidly, and it is principally the 
action of this juice that makes the digestion in the small 
intestine so important. 



Fig. 55. Diagram of a longitu¬ 
dinal section of a salivary gland. 
A salivary gland is formed by 
folding in the lining of the mouth 
in the same way that a gastric 
gland is formed by folding in the 
lining of the stomach. The dif¬ 
ference in the plan of the two 
glands is that a gastric gland 
branches only a few times, while 
a salivary gland has hundreds of 
branches. 






THE DIGESTIVE ORGAN'S 


99 


The Liver. The liver is the largest gland in the body; 
it weighs from three and a half to four pounds. It lies in 
the right side of the abdominal cavity close up to the dia¬ 
phragm, one lobe running down close to the body wall and 
another extending across under the diaphragm and covering 
the inner end of the stomach. The liver cells secrete bile , 
and running all through the liver is a system of little ducts 
that collect the bile and bring it all to one large bile duct. 
This large duct empties into the upper part of the small 
intestine. 

On the under side of the liver is a little pear-shaped sac, 
called the gall bladder (Fig. 48). When digestion is not 
going on, the opening of the bile duct into the small intestine 
closes, and the bile passes into the gall bladder, where it is 
stored. Then when food passes into the small intestine for 
digestion, the mouth of the bile duct opens and the walls of 
the gall bladder contract, sending into the intestine a flood 
of greenish-yellow bile. In a later chapter we shall study 
about other important functions of the liver. 

The Digestive System as a Whole. The alimentary canal 
may be compared to a long channel through the body, and 
the cells of the digestive organs to workers who are stationed 
along the sides of the canal to prepare the foods for use by 
pouring digestive juices over them as they pass along the 
canal. 

In the mouth the food is ground into fine pieces and mixed 
with saliva, and the ptyalin in the saliva immediately starts 
the process of digestion. Then the journey through the long 
canal begins in earnest, the cells of the stomach, intestine, 
pancreas, and liver pouring in their juices as the food reaches 
their parts of the canal. On and on the food is moved, the 
juices digesting it and the digested portion being absorbed, 


IOO 


HUMAN PHYSIOLOGY 


until finally only the indigestible matter of the food stuffs 
remains. 

The digestive juices can work outside of the body as well 
as in the alimentary canal, and it might be possible to arrange 
a digestive system according to a plan differing from that 
which nature has used in our bodies. Yet you would have 
difficulty in thinking of anything simpler or better for diges¬ 
tion and absorption than a long tube through the body, into 
which the foods can be taken and soaked in digestive juices 
while they are slowly moved along. 

The Nervous Control of the Digestive System. The diges¬ 
tive organs, like other parts of the body, are controlled by 
the nervous system. Most of the work of regulating these 
organs is done through the sympathetic nervous system, and 
it is carried on without our knowledge and without any atten¬ 
tion from the mind. The salivary glands and the glands of 
the stomach, however, are controlled to a certain extent by 
the higher centers of the brain, and the mind has a very great 
effect on them. You perhaps know how, when you are hun¬ 
gry, the sight or odor of food will “ make the mouth water.” 
This means that at the mere thought of food the nervous 
system starts the salivary glands to work. The gastric 
glands also are influenced by the mind, as the following 
experiments on a dog showed: 

The esophagus of a dog was divided, and when the animal 
was hungry, he was given some fresh beef. The dog thought 
he was eating a good dinner, but a tube had been connected 
to the esophagus in such a way that the beef did not go into 
the stomach but into a dish beside the dog. Nevertheless, 
the gastric glands promptly began to pour gastric juices 
into the stomach. Merely showing the food to the dog was 
enough to start the secretion of the glands. The experiment 


THE DIGESTIVE ORGANS 


IOI 


showed clearly that the mind affects the glands of the stomach 
as well as the salivary glands. 

At another time a tube was fitted to the part of the esopha¬ 
gus which was connected with the stomach, and beef was 
introduced into the stomach without the dog’s knowing that 
he was being fed. In this case, the gastric juice was 
secreted very slowly, and the meat lay in the stomach a long 
time before it was digested. 

These experiments show plainly that the nervous system 
has a great effect on the digestive organs, since the taste or 
smell of food, or even the sight of food, will start the 
secretions to flowing from some of the digestive glands. 
They teach us that it is very important for our food to be 
pleasant to the taste, in order that a good supply of juices 
may be secreted to digest it. They show how indigestion 
may be caused by eating food which is distasteful, and by 
eating when food is not wanted. They also explain some 
things which have long been known, — that a cheerful, happy 
life brings with it a good digestion; and that anger, quarrel¬ 
ing, melancholy, sorrow, homesickness, and pain interfere 
with the digestion of the food. Our food should therefore 
be well cooked and served in an appetizing manner; every 
one should come to the table in a cheerful frame of mind, 
and should avoid all disagreeable topics of conversation, and 
all unpleasant thoughts should be laid aside until the meal is 
over. “ Laugh and grow fat ” is a wise old saying which we 
would do well to heed. 

Alcohol and the Digestive Organs. Strong alcohol is ex¬ 
ceedingly injurious to living cells. The stomach and the 
liver get in its strongest form the alcohol which is taken into 
the alimentary canal, and these are the digestive organs most 
injured by alcohol. Strong alcoholic drinks taken into the 


102 


HUMAN PHYSIOLOGY 


stomach cause inflammation of the lining of the stomach. If 
taken often, they may cause catarrh of the stomach. They 
are especially harmful if taken when the stomach is empty. 
Alcohol taken at mealtime is diluted by the food and liquids 
in the stomach, and its effect on the mucous membrane of 
the stomach is therefore weakened. Practically all alcohol 
taken into the alimentary canal is absorbed through the stom¬ 
ach walls, and therefore the intestine is little affected by it. 

After the alcohol is absorbed from the stomach it is car¬ 
ried to the liver. The two chief diseases of the liver, due to 
alcohol, are fatty degeneration, caused by beer, ale, and other 
malt liquors, and hardening of the liver, caused by whisky, 
gin, rum, brandy, and other distilled liquors. In fatty degen¬ 
eration, the living protoplasm of the liver cell is replaced by 
fat, and finally each cell becomes a little sac of fat, unable 
to manufacture bile or to do the other work of a liver cell. 
In hardening of the liver, the connective tissue of the organ 
grows far too abundantly, and by contracting squeezes the 
delicate blood vessels and liver cells. This greatly hinders 
the work of the liver, and may even cause the liver cells to 
waste away and die. Either one of these diseases may cause 
death, hardening of the liver being a common cause of death 
among excessive drinkers. 

THE DIGESTIVE ORGANS OF OTHER ANIMALS 

A starfish throws its stomach out of its mouth and wraps 
it about the oyster or other animal that it wishes to eat. 
A snake has jaws fastened together with ligaments so elastic 
that it swallows whole animals thicker than its own body. 
An elephant feeds itself with its trunk, which corresponds 
to the nose in other animals. There are many other things 


THE DIGESTIVE ORGANS 


103 


connected with the digestive systems and food habits of ani¬ 
mals that are very different from anything that is found in 
man. 

Teeth. Beetles, grasshoppers, and crustaceans 1 have no 
teeth, but have horny jaws which work sideways instead of up 
and down as our jaws work. Some fish have teeth, but many 
have none. A frog has teeth in its upper jaw, and a toad 
has no teeth in either jaw. All the reptiles have teeth ex¬ 
cept the turtle tribe, which, like the birds, have horny, tooth¬ 
less beaks. In the poisonous snakes, two of the salivary 
glands secrete poison, or venom, instead of saliva, and two of 
the teeth are long, hollow fangs through which the venom is 
injected into whatever the snake strikes. 

The teeth of mammals differ very much according to the 
food which they eat. Rodents have long, chisel-like incisors 
for gnawing. The carnivora have long canines for killing 
their prey and tearing the flesh on which they feed. The 
herbivora have broad back teeth for grinding the grass and 
leaves which they eat. 

Among the herbivorous animals are many interesting 
differences in the number and arrangement of the teeth. An 
elephant has ten teeth,—two upper incisors (the tusks) and 
eight molars. A cow has six incisors and two canines in the 
lower jaw, and no incisors or canines in the upper jaw. A 
horse has six incisors and two canines in each jaw, but the 
canines do not come through until about the sixth year. You 
can therefore tell something about the age of a horse by 
looking at his teeth. If he has eight front teeth in each jaw, 
he is over six years old. In both the cow and the horse there 
is a wide space between the canines and the back teeth. 


1 Hard-shelled animals with Jointed legs, like the crab, crayfish, lobster, etc. 


104 


HUMAN PHYSIOLOGY 


Tongues. A frog’s tongue is fastened near the front of the 
mouth, and lies with its tip pointing backward in the mouth. 
So quickly that the eye cannot follow it, the frog can throw 



Fig. 56. A frog’s tongue. 

its tongue over forward and out of its mouth to catch an 
insect. The lizard also catches insects by shooting out the 
tongue. In this way some small lizards pick up from one 
thousand to fifteen hundred ants at one feeding. A snake 
uses its forked tongue for feeling, and possibly for frighten¬ 
ing away those who might attack it; but a snake does no 



Fig. 57. A chameleon catching a moth. The chameleons are closely related to the 
lizards. The tongue can be extended six or eight inches with lightning-like rapidity. 


harm with its tongue. The tongues of carnivorous mammals 
are covered with sharp little points for cleaning the last 
particles of meat from bones. The giraffe can stretch out 
its tongue until it is eighteen inches long, to gather in the 
leaves on which it feeds. 







THE DIGESTIVE ORGANS 


105 


Other Digestive Organs. Crustaceans have a gastric mill 
in the stomach. On the inside of the stomach wall there are 
bony plates which are rubbed together to grind up the food. 
A chicken (like other birds) softens its food in a crop , or wide 
place in the esophagus, and then, with small stones which it 
swallows, grinds the food in the gizzard , or thick-walled back 
part of the stomach. 

The ruminants , or cud-chewing animals (cattle, sheep, 
goats, deer, antelope, camels, and giraffes), have the stomach 



Fig. 58. The stomach of a ruminant. 


in four parts or divisions. They have also two openings from 
the esophagus into the stomach, one a longitudinal slit in the 
side of the wall opening into the first division of the stomach, 
and the other the usual opening at the bottom of the 
esophagus leading into the second stomach. The food is 
first swallowed without much chewing, and the ball of grass 
or other coarse material stretches the esophagus wall, opens 
the slit in its side, and drops into the first division of the 
stomach. It is either stored here or passed on into the sec¬ 
ond division and stored there. Then, when the animal has 
finished eating, the food is brought up, a mouthful at a time, 








io6 


HUMAN PHYSIOLOGY 


and rechewed. When it is swallowed the second time it is 
so soft and pasty that it fails to open the slit in the esophagus 
wall, but passes through the upper part of the second division 
of the stomach into the third stomach. From there it is 
quickly passed into the fourth or true stomach, where it is 
digested. 

In their wild state the cud-chewing animals are eaten by 
the carnivora, and this kind of stomach is an advantage to 
them, since they can gather their food quickly and swallow 
it, and then hide in a safe place while they chew it at their 
leisure. 

In addition to the four divisions found in the stomachs of 
other ruminants, the camel has little sacs, formed by folding the 
stomach wall into pouches or pockets, in which water is stored. 
A muscle runs around the mouth of each sac and closes it 
tightly, holding the water in until it is needed. At the right 
time the muscle closing the sac relaxes, letting the water flow 
into the stomach. 

The intestine of the carnivorous animals is short, and that 
of the herbivorous animals long, the ox having an intestine 
about one hundred and fifty feet in length. Judging from the 
human teeth and other digestive organs, man seems to be mid¬ 
way between the herbivorous and carnivorous animals. We 
may therefore conclude that nature intends that man should 
eat both vegetable and animal food. 

Summary. Before the foods can be used by the cells they 
must be digested. This work is done by the organs of the 
digestive system, which is composed of the alimentary canal 
and the accessory organs of digestion. In the main the 
digestive organs are glands that take material from the blood 
and manufacture digestive juices. 

The alimentary canal is nearly thirty feet in length. It 


The digestive organs 


107 

has muscles in its walls that move the food onward, and is 
lined with mucous membrane. The stomach holds about 
three pints. It serves as a storehouse for food, and the 
glands in its wall secrete the gastric juice. The gastric juice 
contains pepsin for digesting proteid foods, and acid which 
assists in digestion and kills bacteria. The small intestine 
is about twenty-two feet in length. Its glands secrete the 
intestinal juice, and the villi on its walls absorb the digested 
food. The glands of the large intestine secrete mucus and 
throw off wastes from the body. 

The body of a tooth is composed of dentine. Its crown is 
covered with hard enamel and it has a pulp cavity in its 
center. The four kinds of teeth are incisors, canines, bicus¬ 
pids, and molars. There are twenty teeth in the temporary 
set and thirty-two in the permanent set. Decay of the teeth 
is caused by bacteria that grow in the food material that clings 
to the teeth. To prevent decay, keep the teeth clean. 

There are three pairs of salivary glands, — the sublingual, 
submaxillary, and parotid. They secrete saliva which 
moistens the food and contains ptyalin for digesting starch. 
The pancreas pours pancreatic juice into the small intestine. 
This juice contains trypsin for digesting proteid, amylopsin 
for digesting starch, and steapsin for digesting fat. The 
liver secretes bile, which is stored in the gall bladder until 
needed in the small intestine. 

The alimentary canal is a long channel through the body 
into which the food is taken and moved along, while diges¬ 
tive juices are poured over it. As the food moves along it is 
digested and absorbed. The salivary glands and the stomach 
are greatly influenced by the mind, and a contented, happy 
life greatly aids in keeping the digestive organs in good con¬ 
dition. 


io8 


HUMAN PHYSIOLOGY 


Alcohol causes inflammation of the stomach and fatty degen¬ 
eration and hardening of the liver. It is exceedingly in¬ 
jurious to the digestive organs and should not be taken into 
the alimentary canal. v 

The digestive organs of some other animals are very dif¬ 
ferent from our own. 


QUESTIONS 

Why do we need a digestive system ? What does the digestive 
system include ? Name the accessory organs of digestion. Describe 
the alimentary canal. What is the function of the teeth? of the 
other accessory organs of digestion? Of what in the main is the 
digestive system composed? 

How are the cells arranged in a simple gland? What do these 
cells do ? What is meant by the word secrete ? secretion ? 

How long is the alimentary canal? Name its chief divisions. 
How is the food moved through it? With what is it lined? How 
does this differ from skin? 

Locate the stomach (page 17). Trace the course of the food into 
the stomach. How much will the stomach hold ? Give its dimen¬ 
sions when full. What two functions has the stomach ? 

What is the function of the gastric glands ? Show how a gland is 
formed in the wall of the stomach. How much gastric juice is 
secreted in a day? What does it contain? What is the use of the 
pepsin? Give two uses of the acid. Describe the muscles of the 
stomach. What two functions have these muscles? What and 
where is the pyloric muscle and what is its function? 

How long is the small intestine? What do its glands secrete? 
What juices are emptied into it? Describe the villi. What is their 
function? What and where is the vermiform appendix? What is 
the function of the glands of the large, intestine? 

Name the parts of a tooth. What is the enamel? dentine? the 
pulp cavity? What is in the pulp cavity? Name the four kinds of 


THE DIGESTIVE ORGAN'S 


iog 


teeth. Give the function of each kind. How many teeth in the 
temporary set? in the permanent set? What causes decay of the 
teeth? How can decay be prevented? After decay has started, 
what should be done ? 

Name the salivary glands. What is their function? What two 
uses has saliva? Locate the pancreas (page 17). What does it 
secrete? What three substances are in the pancreatic juice? What 
does each digest? Locate the liver. How large is it? What does 
it secrete ? Where is the gall bladder and what is its function ? 

To what may the digestive system as a whole be compared ? What 
happens to food as it is moved through the alimentary canal? 

What proof is there that the mind affects the secretion of the 
salivary glands ? In the case of the dog, what effect on the gastric 
glands had the idea that he was eating? What happened when the dog 
was fed without knowing it? What do these experiments show? 
Name some of the conditions of the mind that may interfere with 
digestion. 

What effect has alcohol on the stomach? on the liver? 

How does a starfish get its food into its stomach? What is peculiar 
about the way a snake eats? about the way an elephant eats? Tell 
something about the teeth of different animals. 

What is peculiar about the tongue of a frog? Tell something 
about the tongues of other animals. 

What is peculiar about the treatment of the food in the stomach 
of a crustacean ? of a bird ? Describe the stomach of a ruminant and 
the course of the food through it. Of what advantage is this kind 
of stomach to a ruminant ? Describe the stomach of a camel. 


If the small intestine had a smooth wall, how long would it need 
to be to have the same absorbing surface that it now has (see footnote, 
page 94) ? Explain how folding the wall of the alimentary canal into 
deep glands greatly increases the secreting surface. 



CHAPTER IX 


<3 


DIGESTION, ABSORPTION, AND OXIDATION OF FOODS 1 

Why Food must be digested. When food has been taken 
into the alimentary canal, it has not yet really entered the 
body, but is only in a passageway which leads through the 
body. To get into the body, it must first pass through 
the lining of the alimentary canal into the blood. Many of 
our foods must have changes made in them before they can 
do this, and the following experiments will show one of the 
changes which is necessary.in many foods: 

Drop a few grains of salt into a 
glass of water and stir it up. Does 
the salt dissolve ? Taste the water. 
Are there salt molecules in all parts 
of the water ? 

Stir some clean sand into another 
glass of water. Does the sand dis¬ 
solve? Do its molecules separate 
and go out through the water as 
do the salt molecules, or do they 
remain together? 

Fold a piece of soft paper in 
the manner indicated in Figure 59. 
Open it at the free corners and set 
it in the mouth of a glass. Pour' the salt water into the paper. Does 

1 To the Teacher : The whole subject of the nutrition of the human body is 
far from elementary, and it takes careful teaching to give beginning classes any 
comprehension of it. It is the central idea in physiology, however, and under¬ 
lie) 











DIGESTION ,; ABSORPTION\ AND OXIDATION ill 


the water pass through the paper ? Does the salt pass through the 
paper? Arrange another piece of paper the same way and pour into 
it the water containing sand. Does the sand pass through the paper ? 

When a substance dissolves in a liquid, its molecules 
separate. When it does not dissolve, they remain clinging 
together in a great mass. The single molecules of salt in 
the water readily pass through the paper; but the grains of 
sand, with their molecules all in great clusters, are caught by 
the paper and are not allowed to pass through. 

Most of our solid foods are substances that do not dissolve 
in water or in the juices of the alimentary canal. Meat, 
butter, eggs, or bread would lie indefinitely in the alimentary 
canal without dissolving if their molecules were not changed. 
They must, therefore, be digested , or changed to substances 
that will dissolve in the stomach and intestine. Digestion 
is the process of changing foods mto substances that will dis¬ 
solve and pass through the walls of the alimentary canal into 
the blood. 

You will see at once the tremendous importance of diges¬ 
tion, for if it is not properly performed, the food which should 
nourish the body may simply pass through the alimentary 
canal and never get to the cells which it should feed. 

Changes in the Food during Digestion. The molecules of 
food are large, as molecules go, a starch molecule having in it 
four hundred and fifty atoms, while some of the great proteid 
molecules are composed of more than two thousand atoms. 
During digestion these large molecules are split into smaller 
molecules . Each molecule of starch is split into ten molecules 
of malt sugar , and then each molecule of malt sugar is split 

lies practically all hygiene. Additional material on this subject is given in the 
Appendix, and where sufficient time is given to the subject, this material should 
be used. 


112 


HUMAN PHYSIOLOGY 


into two molecules of grape sugar . Thus in digestion, starch, 
which does not dissolve in water, has each of its great mole¬ 
cules split up into twenty molecules of grape sugar, which 
dissolves and passes through the intestinal wall. The great 
proteid molecules and the molecules of fat are also split in 
digestion into smaller molecules which can be absorbed. 

How the Molecules are split. In the digestive juices are 
very peculiar substances called enzymes or ferments ,— the 
ptyalin, pepsin, trypsin, amylopsin, and steapsin that have al¬ 
ready been mentioned. These enzymes have the power of 
splitting up 1 the food molecules. Each enzyme can split the 
molecules of only one class of food, so there must be different 
kinds of enzymes for digesting the carbohydrates, the pro- 
teids, and the fats. 

Digestion in the Mouth. When food is taken into the 
mouth, the salivary glands begin to work more rapidly, and 
the ptyalin in the saliva at once attacks the starch and begins 
to change it to malt sugar. At the best there is not much 
time for digestion in the mouth, and by eating slowly we not 
only give the ptyalin more time to work on the starch, but we 
also give the glands more time to secrete the ptyalin, and 
we mix the ptyalin more thoroughly with the food. All this 
increases starch digestion in the mouth. 

Digestion in the Stomach. The food remains in the stom¬ 
ach from one to four hours. The main digestion carried 
on here is that of the proteids by the pepsin of the gastric 
juice. This enzyme splits the proteid molecules into smaller 
molecules called peptones, which dissolve in the gastric 

1 Enzymes are found only in living animals and plants, but they can work 
outside of a living body as well as in it. If ptyalin is put into a dish with starch, 
or pepsin with a proteid, digestion will go on in the dish as it does in the alimen¬ 
tary canal. 


DIGESTION,\ ABSORPTION\ AND OXIDATION 113 


juice. The stomach keeps working the food along, and espe¬ 
cially in its lower part keeps mixing the gastric juice with it. 
After about an hour the pylorus opens and lets the more 
liquid part of the food pass on into the intestine. The pepsin 
continues its work on the food remaining in the stomach, 
and as this is sufficiently digested, it is passed on from time 
to time into the intestine. The acid in the gastric juice stops 
the action of the ptyalin on the starch, but in the upper part 
of the stomach the acid sometimes takes an hour to work all 
through the food. There is, therefore, considerable starch 
digestion by the ptyalin after the food leaves the mouth. 

Digestion in the Small Intestine. When the food passes 
into the small intestine, the glands of the intestine secrete 
their juices, the gall bladder contracts and sends the stored-up 
bile into the intestine, and the pancreas begins to send in the 
pancreatic juice with its three powerful enzymes,—trypsin, 
amylopsin, and steapsin. Then the following enzymes finish 
the digestion of the foods: 

Amylopsin changes the starches which escape the ptyalin 
into malt sugar. Then each molecule of malt sugar, and also 
the cane sugar (ordinary sugar) that we take in our food, is 
split by enzymes in the intestinal juice 1 into grape sugar. 
Thus all the starches and sugar are finally changed by diges¬ 
tion into grape sugar. 

Trypsin digests the proteids which have escaped the pepsin. 

Steapsin digests the fats. Bile is not a digestive juice, for 
it contains no enzymes; but it assists in destroying the acids 2 

1 The enzyme that digests malt sugar is called maltase. The enzyme that 
digests cane sugar is called invertase. 

2 The intestinal and pancreatic enzymes, like the ptyalin, cannot work when 
strong acids are present. Both the bile and the pancreatic juice contain minerals 
that unite with and destroy the acid of the gastric juice. 


HUMAN PHYSIOLOGY 


ii4 

of the gastric juice, it in some way assists the steapsin in the 
digestion of the fats, and it greatly hastens the absorption of 
the fats. 

Absorption. The liquids and the digested foods in the ali¬ 
mentary canal pass through the wall of the canal into the 
blood. This process is called absorption and takes place 
chiefly from the small intestine. After absorption the blood 
carries the foods, all through the body, and each cell takes 
from the blood the food that it needs. 

The Foods within the Cells. A part of the proteid food 
taken into a cell is used for building purposes. The remainder 
of the food is oxidized (burned) within the cell. In this 
process, the food molecules are torn down and the atoms that 
were in these molecules unite with atoms of oxygen — the food 
molecules are destroyed and new kinds of molecules are 
formed. Therefore, in the oxidation (burning) of the foods 
within the cells, the foods are destroyed and new substances are 
formed. These substances are the body wastes. You must 
get clearly in mind that the same materials (atoms) that go 
into the cells in the form of foods come out of the cells as 
wastes, — that the foods are changed to zvastes within the cells . 

The Body Wastes. When sugar and fat are burned in the 
body, the waste products are carbon dioxid and water. When 
proteid foods are burned or when the protoplasm of the cells 
breaks down, carbon dioxid and water are given off, and in 
addition uric acid and many other waste products are formed. 
The carbon dioxid and the proteid wastes are poisonous and 
pass out of the body through the lungs and kidneys. 

What a Cell gains by burning Food. If the foods simply 
go into a cell and then come out again as wastes, what does 
a cell gain by taking in and burning food? A cell gains 
energy by the oxidation of the foods . 


DIGESTION ,; ABSORPTION, AND OXIDATION 115 


When on a cold day you put coal into the stove, you do not 
care anything about whether or not there is coal in the stove. 
What you are interested in is the heat 
that you will get when the coal burns. 

So when a cell burns food, it is not 
profited by the atoms and molecules 
of the food, but by the energy—the 
heat and strength and power to work 
—that is given to the cell by the 
burning. In this connection it would 
be well to read again pages 78 and 79. 

The Storage of Foods in the Body. 

Our cells must have a constant sup¬ 
ply of food, and it is necessary to 
have a store of food in the body that 
can be used in times of sickness or Wlthin the cell# 
starvation. When sugar is abundant, a few ounces of it can 
be stored by the liver until it is needed by the cells. The 
great store of food in the body, however, is in the form of fat. 
The fat is deposited about the intestines, kidneys, and other 
internal organs, it is packed among the muscles and in other 
tissues, and a layer of fat is laid dowr> under the skin. The 
fat under the skin is useful not only for feeding the body in 
times of food scarcity, but to retain the body heat. 

Fat in Animals. Animals that hibernate go into their win¬ 
ter quarters fat in the autumn, use up their fat during their 
winter's sleep, and come out thin in the spring. The camel 
has a store of fat in the hump on its back, which enables it 
to go for many days without food. Seals, whales, and other 
warm-blooded animals that live in cold waters have a thick 
layer of fat under the skin to keep in the body heat. In a 
whale this layer of blubber is sometimes two feet thick. 



Fig. 60. The foods pass into 
a cell and are changed to wastes 



ii 6 


HUMAN PHYSIOLOGY 


ALCOHOL AND DIGESTION 

Alcoholic Drinks and Digestion. Alcohol taken with food 
causes an increase in the amount of saliva and gastric juice 
secreted, but it seriously interferes with the work of the pepsin 
if more than five per cent of the contents of the stomach is 
alcohol. Alcohol also checks stomach digestion by paralyzing 
the muscles of the stomach, and beer and wine contain acids 
and other substances that very greatly hinder the work of the 
ptyalin. On the whole, the rate of proteid digestion is not 
much changed by alcoholic drinks in small quantities, but 
the digestion of the starch is greatly hindered. The whole 
question of the effects of alcohol on the process of digestion 
is of little practical importance, however, for alcohol so fre¬ 
quently causes diseases of the digestive organs that it would 
be unwise to take it into the alimentary canal, even though 
it greatly aided digestion. 

Effects of Alcohol on the Work of the Liver. The liver 
manufactures bile and stores up sugar. It has besides a 
third function, one connected with the uric acid and other 
proteid wastes of the body. The uric acid is poisonous to 
the body, and if it is not removed from the blood, rheuma¬ 
tism, gout, and other serious troubles follow. The liver 
changes a considerable part of the uric acid to Urea, which is 
taken out of the body by the kidneys. 

Alcohol not only produces the diseased condition of the 
liver so commonly found in alcohol users (page 102), but it 
sometimes interferes especially with the manufacture of urea 
in the liver. In some persons alcohol even in very small 
amounts (the amount that one would get in a glass of beer) 
seriously hinders the liver in its work of changing uric acid to 


DIGESTION ,; ABSORPTION , AND OXIDATION 117 

urea. A large part of the uric acid is then left in the blood 
to bring about its evil consequences. 

Summary. Foods are digested, or split by enzymes, to 
make them dissolve and pass through the walls of the alimen¬ 
tary canal. 

Starch is split into malt sugar by ptyalin in the mouth and 
stomach and by amylopsin in the intestine. The malt sugar 
and the sugar that we eat are split in the intestine into 
grape sugar. This grape sugar is then absorbed and carried 
to the liver, where it is stored until it is needed by the cells. 
Within the cells the grape sugar is burned, and water and 
carbon dioxid come out of the cells as wastes. The cells 
obtain energy from the sugar. 

Proteids are split into peptones by pepsin in the stomach 
and by trypsin in the intestine. They furnish energy and 
building material to the cells, and are broken up into water, 
carbon dioxid, and uric acid, and into a number of other 
substances which contain the nitrogen of the proteid molecule. 

Fats are digested in the small intestine. They are burned 
to carbon dioxid and water in the cells, to which they give 
energy. 

After digestion the foods are absorbed and carried by 
the blood to the cells. Within a cell, part of the proteid 
food is used in building new protoplasm and the remainder 
of the food is oxidized. In this process the food molecules 
are torn down and new substances (the body wastes) are 
formed from the atoms of these molecules. By the oxidation 
of foods a cell gains energy. 

Cells must have a constant supply of food, and there is in 
the body a great store of fat for use in times of sickness or 
when food cannot be obtained. 

Alcoholic drinks increase secretion but hinder the action of 


118 


HUMAN PHYSIOLOGY 


the enzymes, and on the whole make the process of digestion 
slower. They also produce serious results by keeping the 
liver from changing uric acid to urea. 

QUESTIONS 

Why must foods be digested? What is digestion? What kind of 
changes do the food molecules undergo during digestion ? What is 
an enzyme? Name some of the digestive enzymes. 

What enzyme is in the saliva and what kind of food is digested in 
the mouth? To what is this food changed? Give three reasons for 
eating slowly. What enzyme is in the stomach? What kind of 
foods are digested in the stomach? To what are they changed? 
How long does food remain in the stomach ? What do the stomach 
muscles do during this time? What effect has the acid of the 
stomach on the ptyalin ? 

What digestive juices work on the foods in the small intestine? 
Name the three enzymes in the pancreatic juice. What does the 
amylopsin do? To what are all the starches and sugars finally 
changed in digestion? What does the trypsin do? the steapsin? 
What is the function of the bile ? 

What is absorption? Where are the foods taken after absorption? 
In what way does a cell use part of the proteid food? What is done 
with the remainder of the food? What is oxidation? What happens 
to the.food molecules during oxidation? What becomes of the atoms 
that were in the food molecules? 

What wastes are formed when sugar and fat are burned within the 
cell? when proteids are burned in the cell? Which of these wastes 
are poisonous? How do they leave the body? What does a cell 
gain by burning food? 

Why is it necessary to have food stored in the body? Where is 
sugar stored? In what form is the chief store of food in the body? 
Where in the body is the fat deposited? How is fat used by animals 
that sleep through the winter? Where does the camel have a store 


DIGESTION, ABSORPTION, AND OXIDATION 119 

of fat and why does it need this fat? Why do animals that live in 
cold climates need a layer of fat on the body? 

What effect has alcohol on the secretion of saliva and gastric juice? 
on the rate of digestion of proteids? of starch? Why is it unwise 
to take alcohol into the alimentary canal? What are the three func¬ 
tions of the liver? What effect has alcohol on one of these functions? 
What diseases are caused by this ? 


If a cell had fats and carbohydrates, could it live without proteids? 
Why? If it had proteids and fats, do you think it could live without 
carbohydrates, or if it had proteids and carbohydrates, could it live 
without fats ? Give a reason for your answer. 

A man had trouble in digesting fatty food. What enzyme was 
weak in his digestive juices? 

Malt contains an enzyme that does the same work as ptyalin and 
amylopsin. A man who had stomach indigestion took malt to relieve 
the difficulty. What mistake did he make ? What enzyme should he 
have taken? 

Suppose there is trouble in digesting starch. What other food can 
be eaten that will give the cells grape sugar? 

What enzyme is lacking when there is trouble in digesting sugar, or 
sweet materials like candy and cake that contain much sugar? Would 
the use of malt or pepsin relieve the trouble ? Is it possible to furnish 
the cells with grape sugar without eating sugar ? How ? 

What enzymes are mainly employed in digesting the following 
foods : potatoes; maple syrup ; butter; cheese ; beans ; lean meat; 
fat meat? 

Find out what enzymes you can buy in a drug store. Do any ani¬ 
mals have enzymes that we do not have ? Do plants have enzymes ? 



CHAPTER X 


DIETETICS 

What a Food is. A food is a substance that can be di¬ 
gested; 1 that can furnish the cells with either building material 
or energy , or with both building material and energy ; and that 
does not injure the cells. Coal contains energy, and dyna¬ 
mite contains great quantities of energy; but the diges¬ 
tive enzymes cannot split the molecules of coal and dynamite, 
so these substances are of no use for food. Opium can be 
burned in the cells, and of course must furnish heat to the 
cells. Yet opium is not a food but a poison, because the 
injury done by it to the cells is many times greater than 
the good done by the little energy which it yields. A true 
food not only must furnish energy, but also must not injure 
the cells. 

In dietetics we have, therefore, two problems. For our 
food we must choose substances that can be digested without 
injury to the digestive organs , and substances that will supply 
the needs of the body without injuring it. 

KEEPING THE DIGESTIVE ORGANS IN HEALTH 

One of the most important problems connected with our 
diet is that of keeping the digestive organs in health. Not 
only do these organs get out of order easily, but digestive 

1 A few foods, e.g. grape sugar, and some of the ingredients of soups, are in 
such a form when eaten that they can be absorbed without digestion. These, 
of course, need no digestion. 


120 


DIETETICS 


121 


troubles are exceedingly stubborn and difficult to cure. Below 
you will find some of the results and causes of indigestion. 

Results of Indigestion. If food lies in the stomach for a 
long time without digestion, too much acid will collect in the 
stomach. Sometimes the stomach becomes so sour from 
these acids that it throws its contents out to get rid of 
them. Intestinal indigestion is even worse than stomach 
indigestion, so it is a matter of great importance to select 
food that can be digested and moved along the alimentary 
canal in a reasonable time. It is also very important that 
the undigested remains of the foods be cleared out of the 
large intestine daily. If this is not done, bacteria will grow 
in the large intestine and form substances that are very 
injurious 1 to the body. These substances will then be 
absorbed and carried all through the body by the blood, 
causing headaches and the trouble called biliousness. 

Causes of Indigestion, i. Eating too rapidly and not chew¬ 
ing the food into fine pieces . It is exceedingly important that 
the food be broken into fine pieces, so that the saliva will be 
well mixed with it, and so that the enzymes can get at its 
molecules. Large pieces of food not only remain for a long 

1 The importance to the health of the prompt movement of the food along the 
alimentary canal cannot be too strongly emphasized. If the intestinal muscles are 
slow in their work, the bacteria that are always present in the alimentary canal 
will produce offensive gases that will be carried to the lungs and given off in the 
breath, and substances that will poison the whole body will be absorbed from the 
intestine. Nearly all headaches are due either to the eyes or to these substances, 
and it is now thought that some of the very serious diseases of the liver and 
kidneys are due to these same poisons. Coarse vegetables, fruits (especially if 
the skins are eaten), corn meal, oatmeal and whole wheat bread furnish consider¬ 
able amounts of indigestible matter which stimulates the muscles in the walls of 
the alimentary canal, and causes them to move the food along. Drinking consid¬ 
erable quantities of water (most of which should be taken between meals) also 
helps to keep up the movement of the food in the alimentary canal. 


122 


HUMAN PHYSIOLOGY 


time in the stomach and small intestine, but they often pass 
undigested into the large intestine and furnish food for the 
injurious bacteria that grow there. Washing the food down 
with water is a bad habit, for it causes the food to be swallowed 
before it is thoroughly chewed. Bad teeth are another com¬ 
mon cause of serious stomach and intestinal indigestion. 
Why? 

2. Eating more than can be digested in a reasonable time . 
The troubles that arise from allowing food to lie too long in 
the alimentary canal have already been discussed (page 121). 

3. Eating an entire meal of one kind of food. When this 
is done, all the work is thrown on one enzyme. Too much 
fat meat may give the steapsin more work than it can do, 
while the amylopsin is entirely idle because no starchy food 
was eaten. Eating a great amount of candy at one time gives 
the sugar-digesting enzyme more sugar than can be digested 
for hours, while the other enzymes have nothing to do. This 
has exactly the same effect as eating too much, for in either 
case, digestion will be so long delayed that stomach and in¬ 
testinal troubles will follow. School children often injure 
their digestive organs by eating such foods as candy, pickles, 
and pastry. Some of these foods are injurious because they 
are taken in too great quantities, and some are indigestible 
and injurious in any quantity. 

4. Eating irregularly and between meals . After digestion, 
the glands of the alimentary canal should have time to rest 
and prepare a supply of enzymes for the next meal. Eating 
between meals also dulls the appetite at mealtime, and we 
have already seen (page 100) how hunger and a good appetite 
assist in causing an abundant flow of digestive juices. 

5. Iced drinks. Warm soup taken at the beginning of a 
meal warms the stomach and starts the flow of the gastric 


DIETETICS 


123 


juice. Ice water and iced tea taken with the meals chill the 
stomach and hinder the secretion of the gastric juice. Ice- 
cold soda fountain drinks are decidedly injurious if taken 
frequently or in large amounts, and cool drinking water is 
more healthful than water that is ice-cold. 

6 . Unappetizing and poorly cooked food. If not properly 
cooked, some foods are hard to digest (page 128), but the 
greatest evil in bad cooking is that the food is not pleasant 
to the taste, and the digestive juices are not secreted abun¬ 
dantly. Jams, jellies, soups, and some other foods contain 
little nourishment, and are important chiefly because they 
make it possible for us to eat with a relish and to digest large 
quantities of rather tasteless but very nourishing foods like 
bread. 

7. Talking and thinking about unpleasant things at meal¬ 
time. This interferes with the secretion of the digestive 
juices (page 101). 

8. Hard exercise or study immediately before or after eating. 
This takes the blood away from the digestive glands when 
they need it to manufacture the digestive juices. 

9. Lack of exercise . Any one who does not exercise is 
almost certain to suffer from indigestion (page 73). 

10. Overwork or overstudy. Either one of these will bring 
on indigestion. Probably the nervous system is first injured, 
and the trouble with the digestive organs comes from a lack 
of proper nervous control. 

11. Trouble with the eyes . Many cases of headache 
and stomach trouble are cured at once by fitting the eyes 
with proper spectacles or eyeglasses. Probably bad eye¬ 
sight, like overwork, injures the nervous system, and the 
nervous system then fails properly to regulate the digestive 
organs. 


124 


HUMAN PHYSIOLOGY 


AMOUNT AND KINDS OF FOOD NEEDED 

Amount of Food needed. A healthy man of aVerage weight 
(154 pounds), usually eats about 4 ounces of dry proteid food 
a day. Whether he works or not this amount of proteid 
is eaten. 

In addition to the proteid that he eats for building material, 
a man must have food for energy. The amount he will need 
for this depends on how much work he does and on whether 
or not he is exposed to the cold. A hard-working man 
usually eats twice as much as a man who does light work; 
and some lumbermen, who were doing heavy work in the 
Maine woods in the cold of winter, were found to be eating 
more than three times as much as is needed by a bookkeeper 
or a tailor who does light indoor work. 

A Mixed Diet Best. Only the proteids furnish building 
materials, but any kind of food furnishes energy. A man 
could eat nothing but proteid, but so much of one kind of food 
would be sure to cause indigestion, and the system would be 
overloaded with proteid wastes (page 114). It is therefore 
better to take only enough proteid to furnish building mate¬ 
rial and to use carbohydrates and fats for energy foods. 

Fats give more than twice as much heat as the carbo¬ 
hydrates give, and the Eskimos and other peoples living in 
cold climates eat chiefly proteid and the fat of animals. The 
people of warm climates live principally on proteids and car¬ 
bohydrates, which they get from vegetables and fruits. Pro¬ 
teids and either one of the energy foods will do, but it is 
better for the digestion to take both fats and carbohydrates. 
An additional reason for always eating some fat is that the 
body seems more liable to certain diseases, among them con¬ 
sumption, if the amount of fat in the diet is very small. 


DIETETICS 


125 


Mistakes in Diet from the Standpoint of Health. The three 

most common mistakes in diet, from the standpoint of health, 
are eating in stick a way as to cause indigestion , eating either 
too much or not enough proteid , and not eating enough fat . 

The vegetable carbohydrates are the cheapest of all foods, 
and among the very poor, families sometimes live almost en¬ 
tirely on them and fail to get enough proteids and fats. The 
poor peasants of some European countries who live chiefly 
on potatoes and other vegetables, have not the same strength 
for their work that American workmen have who eat meat, 
butter, eggs, and wheat bread, in addition to vegetables. 
On the other hand, the proteids are the most appetizing of 
all the foods, and among the wealthier classes too much 
proteid is often eaten. The old English gentlemen used to 
feast largely on venison and beef, and this, with their wine¬ 
drinking, gave them gout, rheumatism, and kidney and liver 
trouble. Among Americans, the two most common mistakes 
in diet are eating too much or too little proteids, and not 
eating enough fats. 

Mistakes in Diet from the Standpoint of Economy. In 

oysters we pay over $5 for a pound of proteid, while in 
bread the same amount of proteid can be bought for 70 
cents. If a man has a good appetite and strong digestive 
organs, and only a little money, it is plain that he had 
better buy his proteids in bread, and not in oysters. Also, 
in beef at 14 cents a pound we pay more than three times as 
much for energy as we pay for energy in potatoes at 75 cents 
a bushel. It is therefore cheaper to use potatoes for energy 
food than the more expensive proteid foods like beef. 

Buying foods out of season is another economic mistake 
made by many people. A box of strawberries may cost 
30 cents at the beginning of the season, and in three weeks 


126 


HUMAN PHYSIOLOGY 


it may be possible to buy three boxes for 30 cents. If a per- 
son has not a great deal of money and wants strawberries, 
he should not spend 30 cents for one box, but should wait 
until he can get three boxes for 30 cents. Economy in buy¬ 
ing foods is an important matter, for the average family is 
not wealthy, and money that is badly needed for other pur¬ 
poses is often spent in buying foods when they are out of 
season, and in buying expensive foods when cheaper foods 
would do as well from the standpoint of health. 

Following a Healthy Appetite. From all that you have 
now learned you know that a healthy diet must contain the 
proteids, carbohydrates, and fats in such proportions that 
they will give the body its building materials and energy, and 
at the same time will not burden it with proteid wastes or 
cause trouble in the alimentary canal; and that our food must 
be properly cooked or otherwise prepared to make it appetiz¬ 
ing, or it will not be digested. 

If you will stop to consider, you will see that in following 
a moderate, healthy appetite, we shall very likely get about 
the things that we need. We eat lean meat to give us proteid, 
and bread or potatoes with it to furnish carbohydrates. We 
like a little butter with our bread, and that gives us some fat, 
and if we have no fruit or fresh vegetables for some time, we 
become hungry for them. When the body needs anything, 
the appetite will usually let us know. 

Yet we must remember that some individuals have an 
appetite for green fruit and other unhealthful substances, 
and that other persons get into the habit of eating far more 
of certain staple foods, especially of meats, than the body 
needs. The appetite can be followed only when it is really 
a healthy appetite and calls for those things that are needed 
to keep the body in health. 


DIETETICS 


12 7 


Mistaken Ideas in Regard to Foods. Several mistakes in 
regard to foods are common throughout our country. One 
is that there is a difference between vegetable and animal 
foods. Animal foods usually have less refuse matter in them 
than vegetable foods, and are often more easily digested ; but 
there is no reason to think that in nourishing the body, animal 
food differs from vegetable food. 

Another idea that has no foundation in truth is that the 
cells of the brain require different food from the other cells 
of the body. Still another is that certain breakfast foods 
made from grains are particularly valuable as foods. They 
contain only the carbohydrates and proteids that were in the 
grain from which they were made, and their food value is 
about the same as the food value of an equal weight of bread. 
They are clean, digestible, and nutritious foods, but lack the 
wonderful properties claimed for them in some advertise¬ 
ments. 

Another thing long believed to be true was that whole 
wheat bread is more valuable than ordinary white bread. It 
is true that whole wheat bread contains more proteid than 
the bread made from the inner part of the grain, but it is not 
so digestible; and it has been found that the body gets more 
proteid out of a pound of white bread than out of a pound of 
brown bread. Still another mistake is to suppose that beef 
tea is very nourishing. In reality it contains almost no nutri¬ 
ment. It is appetizing and stimulating, and is often very 
valuable to a sick person because it enables him to take and 
digest other food, but beef tea alone should not be depended 
on for nourishment in any long-continued illness. 

Another idea common among intelligent people is that we 
might live much better and more economically if we would 
change our diet and eat chiefly nuts, bananas, beans, or some 


128 


HUMAN PHYSIOLOGY 


other article not commonly used as one of our main foods. 
This idea does not seem to be correct. The starch in bananas 
is raw, and is difficult of digestion. Beans are very rich in 
proteid, but they are hard to digest, and if eaten in large 
quantities, disagree with many people. Nuts are also diffi¬ 
cult to digest and in large quantities give too much fat for 
most people. Some persons keep their health on these foods; 
but man has been testing the different foods for thousands 
of years, and long ago he learned which ones are best for 
the average person. The flesh of animals, milk, eggs, grains, 
potatoes, and a few other vegetables make up the bulk of the 
world’s food, other things being used in smaller quantities. 

Cooking. Cooking makes many foods more appetizing , and 
thus causes a greater flow of the digestive juices. Cooking 

also makes many foods more di¬ 
gestible . By cooking, vegetables 
and the connective tissue fibers 
of meats are made more tender. 
This causes the vegetables and 
meats to fall to pieces more 
easily, and the digestive juices 
are thus given a better oppor¬ 
tunity to do their work. 

Cooking is especially impor¬ 
tant in the case of starchy foods, 
because raw starch is in hard little 
grains which the digestive juices 
cannot penetrate, and which the 
enzymes break up very slowly. Raw starch, therefore, is 
almost indigestible. Cooking the starch grains causes them 
to soften, swell, and burst. The enzymes are then able to get 
in among the starch molecules to digest them. 



Fig. 6i. Starch grains in the cells 
of a potato. 


DIETETICS 


129 


Frying. Frying is not a healthful way to cook most foods. 
Too much fat in the stomach hinders the secretion of the 
gastric juice, and in frying, the food is coated 
with fat. As the food passes through the 
mouth and stomach it is covered with a 
layer of fat, and this coating of fat is not 
digested off until the intestine is reached. 

The ptyalin and pepsin are thus to a certain 
extent shut off from the food and are not 
able to do their work properly. 

Dangers from Raw Meats. Pork some¬ 
times contains small worms called trichina} 

These when taken 
into the alimen¬ 
tary canal pass 
into the body, 

enter the muscles, fig. 62. a trichina 
and kill the mus- lying among the mus¬ 
cle cells. This deCellS ‘ 
disease is called trichinosis. 

The young of the tapeworm is 
found in both pork and beef. 
When taken into the intestine it 
fastens itself to the intestinal wall 
by small hooks on its head, absorbs 
the digested food in the intestine, and grows into a long 
worm . 1 2 

1 An ounce of pork may contain 80,000 trichinae. Each female produces 
about 1000 eggs in the intestine, which would give about 40,000,000 of these 
small worms from an ounce of pork. The eggs hatch in the intestine and the young 
bore through the intestinal wall, enter the blood, and are carried to the muscles. 

2 Tapeworms often measure several feet, and sometimes several yards, in length. 







130 


HUMAN PHYSIOLOGY 


Meat, especially pork, should be well cooked before it is 
eaten, to kill any parasites that may be in it. When thick 
pieces of meat are fried, the inside parts may not be suffi¬ 
ciently heated to kill everything in the meat, but boiling or 
baking renders meat absolutely safe from parasites. 

Dangers from Bacteria in Foods. In later chapters we shall 
take up the subject of disease germs and learn how the germs 
of typhoid fever, diphtheria, and other dangerous germs are 
carried in foods. It is well for you to understand now, how¬ 
ever, that all decay is due to bacteria, and that as most foods 
form a splendid breeding place for bacteria, they therefore 
quickly decay. In caring for foods, cleanliness , to keep germs 
from getting into them, and cold , to keep the germs from grow¬ 
ing, are the two most important points. Any food that is at 
all tainted is so full of germs that it is unfit for use, and in 
general, the fresher a food is when it is used, the fewer germs 
it has in it. 

Patent Medicines. Often we read, in advertisements, of 
medicines that will cure cancer, consumption, dyspepsia, and 
many other of our worst ills. These medicines will not do 
what is claimed for them. If there were any medicines that 
would cure cancer or consumption, the skillful physicians 
and scientists who are at the heads of our medical colleges 
and hospitals would know it, and they would be using them 
and telling every one about these wonderful remedies. 

Some patent medicines contain opium, which is soothing 
and causes pain to be unnoticed, so that a person sometimes 
thinks he is better when his disease has not been affected at 
all. Other patent medicines are very strong in alcohol, — as 
strong as, or stronger than, the most powerful alcoholic drinks. 
A dose of some of these medicines contains enough alcohol 
to affect the body decidedly, and the strengthening effect 


DIETETICS 


131 

that persons sometimes think they feel when they use these 
“tonics,” is nothing but the effect of the alcohol. Many 
patent medicines of course contain useful drugs, but without 
the advice of a physician it is unwise to take in among the 
delicate little cells of our bodies any strong medicine whose 
effects we do not understand. 

ALCOHOL AS A FOOD 

The question is often asked whether or not alcohol is a 
food. On this point people continually disagree. One rea¬ 
son for the disagreement is that different definitions for the 
word “food” are used. A food is often defined as a sub¬ 
stance which can be burned in the body and will give energy 
to the body. In this sense, alcohol is a food, for in moderate 
amounts it is oxidized in the body and gives heat and strength 
to the muscles. The other definition of a food is that given 
on page 120. This definition insists that a food not only 
must furnish building material or energy, but also must not 
injure the cells. According to this definition, it is certain 
that alcohol in any but very small quantities is not a food* 
for it works great harm to the cells, especially to the nerve 
cells. 

Whether or not alcohol in very small doses injures the 
cells, is very uncertain. If you took a drop of alcohol into 
your body, its effect would be so slight that you could not 
notice it. Even if it injured your cells, you would never 
know it. If you took a spoonful of alcohol, probably you 
still could not notice any effect on yourself. But if you 
began the habit of drinking beer or wine or other alcoholic 
drinks, it is certain that you would get enough alcohol to 
injure your body decidedly. We do not discuss whether 


132 


HUMAN PHYSIOLOGY 


a very, very small amount of a poison like opium or bella^ 
donna would injure the cells, and whether these drugs give 
energy to the cells and are, therefore, foods. There is little 
more reason for discussing whether or not alcohol is a food, 
for, used in the amounts taken by any one who drinks 
alcoholic liquors, it is not a food, but a poison. All sensi¬ 
ble persons know that men do not drink alcohol because 
they think it is a food, and that the question of whether 
alcohol is a food is brought up to find an excuse and not a 
reason for drinking it. Professor Bunge, a great German 
physiologist, chemist, and physician, well knew this and said: 

“ There is never any lack of excuses for taking a drink. 
People drink when they meet; they drink when thfey part. 
They drink when they are hungry to quiet hunger; they 
drink when they are surfeited to arouse appetite. They drink 
when it is cold for warmth; they drink when it is hot to cool 
off. They drink because they are sleepy, to keep awake; 
they drink when they cannot sleep, to induce sleep. They 
drink because they are sad; they drink because they are 
jolly. They drink because there is a baptism; they drink 
because there is a burial; they drink and they drink.” 

QUESTIONS 

What is a food? Why cannot coal be used for food? opium? 
What two points must we keep in mind in choosing our foods ? 

Why is it important that foods be digested within a reasonable 
time ? Discuss some of the causes of indigestion. 

How much proteid does a man need in a day ? On what does 
the amount of other food that a man needs depend ? Why would it 
be unwise to eat only proteid foods ? Could a man live on fats and 
carbohydrates ? Why ? Could he live on proteids and carbohydrates ? 
on proteids and fats ? Which gives more energy, fats or carbo- 


DIETETICS 


133 


hydrates ? In what part of the world do the people eat more carbo¬ 
hydrates? more fats? Is it better to eat only two classes of food or 
all three classes? 

Give three mistakes made in diet, from the standpoint of health. 
What class of people eat too little proteid ? too much proteid ? Men¬ 
tion two mistakes from the standpoint of economy that are made in 
purchasing foods. What is said about following a healthy appetite? 
Discuss some of the mistaken ideas that are held in regard to foods. 

Give two ways in which cooking assists the digestion. What effect 
has cooking on meats and vegetables ? on starch ? Why is frying 
an unhealthful method of cooking? What parasites get into the body 
from meat? How may these parasites be killed? 

What causes decay ir> foods? What are the two most important 
points in caring for foods ? Why are fresh foods more healthful than 
foods that are not fresh? 

What injurious substances do some patent medicines contain? 
Why is it not advisable to take medicine without the advice of a 
physician ? What two definitions are sometimes given for a food ? 
According to which of these definitions is alcohol, except possibly in 
the very smallest quantities, not a food? Why is the discussion of 
whether or not alcohol is a food of little practical importance ? 


A pupil had for lunch lemon pie, cake, candy, and olives. What 
enzyme'would do most of the work in digesting this lunch? What 
important food elements would be present in small amounts in such a 
lunch ? Is it safe to follow an appetite that calls for such a lunch ? 

A pound of carbohydrates is a fair allowance for a man for one 
day, and an eight-year-old boy needs about half as much food as 
a man. A boy of this age ate his dinner and then bought and ate 
a half pound of candy. What enzyme would have the candy to 
digest? How much more work than usual do you suppose the 
enzyme had that afternoon ? Do you suppose the digestion of the 
sugar was finished quickly enough to avoid trouble in the alimentary 
canal ? 



134 


HUMAN PHYSIOLOGY 


REVIEW QUESTIONS 

Chapter VII. Give two reasons why the body needs food. Of 
what is all matter composed ? Of what are molecules composed ? 
What is an element? a compound? Name the three classes of 
foods. Give examples of foods of each class. How do these food 
classes differ in chemical composition? Mention some other things 
that are necessary to the body. 

Chapter VIII. Explain how a gland is formed and how it works. 
Draw a diagram of the digestive system and label the different diges¬ 
tive organs. What is the function of the stomach? of the gastric 
juice? How long is the small intestine? Name three secretions 
that are emptied into it. Describe the villi. What is their function? 
Name the accessory organs of digestion. Define : dentine ; enamel; 
pulp cavity ; incisor; canine ; bicuspid ; molar. 

Name and locate the salivary glands. What is the use of the 
saliva ? What glands of the digestive system are known to be affected 
by the nervous system? What mental condition is favorable to a 
good digestion? What trouble does alcohol cause in the stomach? 
in the liver? 

Chapter IX. Why must food be digested? How are the food 
molecules changed in digestion? By what are they changed? Tell 
where the following enzymes are found, and what food each one 
digests : ptyalin ; pepsin ; trypsin ; amylopsin ; steapsin. To what 
are the proteids changed in digestion ? the starches and sugars ? Why 
must a cell have proteid? What happens to the food molecules when 
the foods are oxidized within the cells ? What becomes of the atoms 
that were in the food? What does a cell gain by burning food? What 
use is the fat in the body? What effect has alcohol on digestion? on 
the work of the liver? 

Chapter X. Define a food. Give some causes of indigestion. 
How much proteid is needed daily? Why is a mixed diet best? 
Mention some common mistakes in diet; some mistaken ideas in 
regard to foods. How does cooking assist digestion? How does 
frying make some foods more indigestible? What two points are 
important in caring for foods? Why are patent medicines dangerous? 
Why, according to our definition of a food, is alcohol not a food ? 


CHAPTER XI 


THE CIRCULATORY SYSTEM 

From the time we are born until we die, the heart beats. 
Day and night the blood flows through the body, passing out 
from the heart, streaming in among the cells, and hastening 
back to the heart. If because of disease or injury to the 
body the heart stops, the body dies. If the blood is weak 
and thin, the health of the body suffers, and if the blood is 
allowed to escape from the body, life at once ceases. 

Why does the heart beat ? Why is the blood kept flowing 
through the body ? How does it help the cells to have the 
blood passing by them ? Why are physicians so anxious that 
the blood be kept strong and pure and that nothing be done 
that will injure the heart ? Why could not the body continue 
to live even though the heart should stop beating and the 
blood should cease to flow ? To answer these questions 
intelligently, we must first of all understand the great laws 
according to which the body lives. Our bodies must have 
food and zvater , they must have oxygen , they must get rid of 
their poisonous zvastes , and they must have an even tempera¬ 
ture t neither too hot nor too cold. Our bodies are composed 
of cells, and each cell must have all of these things. 

The Function of the Blood. The human body is a great 
colony of cells. The food and water for all the cells in the 
colony are taken in through the alimentary canal; but there 
must be some arrangement so that a cell in the brain or in 

i35 


136 


HUMAN PHYSIOLOGY 


the foot can get the food that has been prepared for it by the 
digestive organs. Oxygen is taken in through the lungs 
but the oxygen must be distributed all through the body to 
the cells. The poisonous wastes leave the body through the 
lungs and kidneys; but the wastes that are produced in the 
cells must be moved from the cells to the lungs and kid¬ 
neys before they can be thrown out of the body. The heat 
of the body is produced by burning food within the cells; 
but in certain inner parts of the body, like the liver and 
muscles, there is too much heat, while in the outer parts of 
the body there is not enough heat. There must, therefore, 
be some way of distributing the body heat so that none of 
the cells will be either too hot or too cold. 

The function of the blood is to carry food , water , and oxygen 
to the cells , to carry zvastes azvay front the cells , and to carry 
heat from the warmer to the cooler parts of the body. As the 
blood flows among the cells it feeds them and gives them 
oxygen, picks up and carries away their wastes, cools the hot 
cells, and warms the cells that are too cold. The body may 
be very quickly killed by stopping the flowing of the blood 
among the cells. 


THE CIRCULATORY ORGANS 

The flowing of the blood through the body is called the 
circulation. The organs concerned in keeping up the circu¬ 
lation are the circulatory organs. These are the heart (Fig. 
70), the blood vessels ( arteries , veins , and capillaries ), and the 
lymphatic vessels (Fig. 66). 

The Heart. The heart 1 is usually about the size of the 
closed hand of the person to whom it belongs. It lies in the 

1 The heart is inclosed in a double-walled sac called the pericardium. (Fig 

82.) 



THE CIRCULATORY SYSTEM 


13 7 


thoracic cavity with its apex (point) to the left of the center 
of the body. The walls of the heart are composed of muscle 
cells, and within the heart are four cavities, — two upper 
cavities called auricles , and two lower cavities called ventri¬ 
cles. The auricles have thin walls, for their task is the small 
one of sending the blood down into the ventricles. The ventri- 



FiG. 64. Diagram of the right side of the heart showing the working of the valves. 
When the ventricle relaxes, the valves are as shown in A. When the ventricle con¬ 
tracts, the valves are as shown in B. 

cles, on the other hand, have thick walls because they have 
the heavy work of forcing the blood through the body. The 
function of the heart is to keep the blood circulating through 
the body. 

The Action of the Heart. Place your hand on your chest 
and you can feel the heart beat . 1 What is it doing when it 
beats ? It is pumping the blood through the body. 

The walls of the auricles first contract and draw inward on 

1 When the ventricles contract, the apex of the heart is pressed more forcibly 
against the wall of the chest. This causes the beat, which can be felt by placing 
the hand on the chest over the heart. The pulse that is felt in the arteries is a 
wave that travels out in the blood within an artery when the ventricles force the 
blood out of the heart. 





PULMONARY VEINS 


HEPATIC VEIN 


HEPATIC ARTERY 


LIVER_ 


PORTAL VEIN 


CAPILLARIES 
OF LEGS 


CAPILLARIES OF 
CHEST AND ARMS 


DESCENDING VENA £AVA 


PULMONARY ARTERY 


RIGHT LUNG 


CAPILLARIES OF 
STOMACH. INTESTINE 
AND SPLEEN 


CAPILLARIES 
OF HEAO 


LEFT LUNO 


PULMONARY VEINS 


RIGHT AURICLE 
RIGHT VENTRICLE 


ASCENDING VENA CAVA 


LEFT AURICLE 
LEFT VENTRICLE 


DESCENDING 

AORTA 


. Diagram of the circulation of the blood in the body. 


138 


Fig. 65 


















I 



Fjg. 66. ITie heart and the principal vessels of the body. 


*39 

























140 


HUMAN PHYSIOLOGY 


the blood, forcing the blood into the ventricles. The auricles 
then relax and the powerful walls of the ventricles contract, 
squeezing the blood out into the arteries. The ventricles 
now relax and for a moment the heart rests. Then the 
auricles again contract, completing the filling of the ventricles; 
the ventricles squeeze the blood out into the arteries, and so 
the process is repeated again and again. In one day the heart 
does as much work in sending the blood through the body as 
its owner would do in walking eight and one half miles on a 
level road. 



Fig. 67. These gates work like the valves of the heart. When the boy pushes on 
them one way, they open, but when he pushes on them the other way, the chains hold 
them so that they will not open. 


The Rate of the Heart Beat. In an adult the heart usually 
beats from seventy to eighty times a minute. It is faster in 
women than in men, and varies in different individuals, some 
persons naturally having a faster heart beat than others. 
The rate of the heart beat varies also with age , 1 with rest and 
•exercise, and with health and disease. You should count 
your own heart beat several times so that you will know its 
average rate. Then in sickness you will know how much it 
varies from its natural beat. 

1 The heart beat at different ages is about as follows: at birth, 130-140; first 
year, 115-130; second year, 100-115; third year, 90-100; seventh year, 85-90; 
fourteenth year, 80-85; adult life, 70-80; old age, 60-70; extreme old age, 
75-8o- 




































THE CIRCULATORY SYSTEM 


141 

The Valves of the Heart. In the heart are four valves, 
two between the auricles and the ventricles (Fig. 64), and two 
at the openings of the great arteries ( aorta and pulmonary 
artery ), which lead out from the ventricles. All four valves 
are made of connective tissue, and their function is to keep the 
blood from flowing backivard. 

The valves between the auricles and ventricles work like 
little doors (Fig. 67) which open only downward into the 
ventricles. Little ligaments hold the valves so that they 
cannot be pushed upward into the auricles. The blood can 
therefore flow from the auricles into the ventricles, but 
when the ventricles contract, the blood pushes up under 
the valves and lifts them so that the openings between the 
auricles and ventricles are closed. Since the blood cannot 
pass back into the auricles, it must flow out into the arteries 
when the ventricle walls contract. 

Each of the valves at the entrance 
to the great arteries is made of three 
loose pockets on the wall of the 
artery. The pockets open upward, 
and as the blood leaves the ventricles 
it readily flows over them. But when 
the ventricles relax and the blood 
starts to run back into the heart, the FlG - 68 - The base of the aorta 
pockets fill with blood and hang out in when the bIood starts t0 flow 
the opening of the artery SO that they backward into the heart it catches 

touch each other. They thus close in the pockets which then swing 
J out and close the opening in the 

the passageway and keep the blood aorta . see also Figure 64. 

from flowing back into the heart. 

Blood Vessels. Arteries are blood vessels in which 
the blood flows away from the heart. Veins are blood 
vessels in which the blood flows to the heart. Capillaries 









142 


HUMAN PHYSIOLOGY 


are small vessels through which the blood flows from the 
arteries to the veins} The two great arteries (aorta and 
pulmonary artery) that leave the heart divide into smaller 
arteries. These smaller arteries divide again and again, 
until finally they end in exceedingly small capillaries, which 



Fig. 69. The blood flows from the arteries through the capillaries into the veins. 


are everywhere among the cells. After running in among 
the cells the capillaries begin to unite. More and more 
of them flow together and form small veins. The small 
veins continue to unite and form larger veins until they 
are joined into the large veins, the vena cava and the 
pulmonary veins , which empty into the heart (Fig. 65). You 
must clearly understand that in the circulation the blood does 
not get out of the blood vessels, but passes through the capil- 

1 To the Teacher : If a microscope can be procured, the teacher should 
not fail to have his pupils observe the fascinating sight of the blood corpuscles 
shooting along in the capillaries. One of the best places to see this is in the 
tail of a tadpole. Lay the tadpole on a flat piece of glass, and it will usually 
become quiet enough in a little while to allow the microscope to be focused on 
the capillaries. 



THE CIRCULATORY SYSTEM 


143 


laries from the arteries to the veins (Fig. 69). So abundant 
are the capillaries that the finest needle thrust into the body 
tissues cuts and breaks many of them. 



RIGHT VENTRICLE 


ASCENDING VENA CAVA 


descending vena cava 


descending aorta 


Carotid arteries 




SUBCLAVIAN ARTERY 
(TO ARM) 

JUGULAR VEIN 
(FROM HEAOl 


subclavian vein 

(FROM ARM) 


LEFT AURICLE 


VENTRICLE 


JUGULAR VE 
(FROM HEAD) 


RIGHT AURICLE 


ARTERY 


SUBCLAVIAN ARTERY 
(TO ARM) 


SUBCLAVIAN 
(FROM ARM) 


F'lG. 70. The heart and the bases of the great vessels. 


The Walls of the Blood Vessels. The walls of the arteries 
are composed chiefly of connective tissue and of muscle 
fibers which are placed circularly about the vessels. When 
the muscle fibers in the wall of an artery contract, they make 
the opening of the artery smaller, and a less amount of 
blood passes through it. By changing the size of the 





144 


HUMA1V PHYSIOLOGY 


arteries, some of the blood 1 can be cut off from a part of the 
body that is resting and needs only a little blood, and can be 
sent to a part of the body that is working and needs a larger 
blood supply. 

The walls of the veins are thinner than the walls of the 
arteries, and have in them more connective tissue and less 
muscle. The walls of the capillaries are very thin, con¬ 
sisting of only one layer of thin flat cells and a few fibers of 
connective tissue. 

The Course of the Circulation. The heart is a double organ. 
The right ventricle sends the blood through the lungs to the 
left auricle. The left ventricle sends the blood through the 
body to the right auricle. In a complete circulation the blood 
therefore passes twice through the heart. By studying the 
diagram on page 138, you will find that the course of the 
blood, beginning with the right auricle, is as follows : 

From two great veins (the venae cavae) into the right 
auricle. 

From the right auricle into the right ventricle. 

From the right ventricle into the pulmonary artery and its 
branches. 

From the branches of the pulmonary artery into the 
capillaries of the lungs. 

From the capillaries of the lungs into four pulmonary veins. 

From the pulmonary veins into the left auricle. 

From the left auricle into the left ventricle. 

From the left ventricle into the aorta and its branches. 

From the branches of the aorta into the capillaries of 
the body. 

1 It is estimated that the capillaries of the intestine can hold all the blood in 
the body, and that if all the vessels in the body should relax at one time, it would 
take several times as much blood as there is in the body to fill all of them. 


THE CIRCULATORY SYSTEM 


145 


From the capillaries of the body into the smaller veins. 

From the smaller veins into the two great veins 1 called the 
ascending and descending venae cavae, and then back into 
the right auricle. 

Day and night the blood circulates through the body, pass¬ 
ing out from the heart through the arteries, flowing through 
the capillaries and returning to the heart by way of the veins. 
Day and night the heart pumps away, 2 keeping the current 
of blood flowing through the vessels. No other organ of the 
body is so hard-worked as the heart, which pauses to rest 
only between its beats. 

The Nervous Control of the Circulation. The heart has two 
sets of nerves, — one set quickening its beat and the other 
set causing it to beat more slowly. Through these nerves, 
the rate of the heart beat is controlled. 

The muscles in the walls of the arteries are also supplied 
with two sets of nerves. One set of nerves causes the 
muscles in the arterial walls to contract, and one set causes 

1 From the diagram on page 138 it can be seen that the portal circulation, or 
the circulation through the liver, is peculiar in that the blood passes through two 
sets of capillaries. The blood that has passed through the capillaries of the 
stomach, intestine, pancreas, and spleen is collected into one great vein (the 
portal vein) and taken to the liver, where it again spreads out in the capillaries 
among the liver cells. It is then collected into the hepatic vein and goes on 
to the heart. Sugar is stored in the liver, and the advantage of this arrange¬ 
ment is that the blood carrying the absorbed sugar passes through the liver 
before it goes to the rest of the body. The blood that comes to the liver through 
the portal vein has lost its oxygen in the first set of capillaries, so the liver has 
another supply of blood coming to it through the hepatic artery (page 138) to 
furnish it with oxygen. 

2 The circulation time of the blood through the body (from left ventricle to 
right auricle) is on an average something like a minute. The circulation time 
through the lungs (from right ventricle to left auricle) is about twelve or fifteen 
seconds. This means that twice in every minute and a quarter the heart must 
pump all the blood in the body through itself. 


146 


HUMAN PHYSIOLOGY 


them to relax. The size of the openings in the arteries, 
and the amount of blood going to the different parts of the 
body, can thus be regulated by the nervous system. 
When a person blushes, the little arteries in the skin of the 



Fig. 71. The vessels of the foot. Only a few of the arteries are shown. 


face open and allow a larger quantity of blood to come into 
them. From this you can understand how quickly the size 
of the arteries can be changed, and, when you think of the 
cause of blushing, you will know that the muscles in the 
blood vessels can be affected by the nervous system. 


THE BLOOD AND LYMPH 

The blood makes up about one nineteenth of the body 
weight. It is composed of a liquid part, the plasma , and 
of red and white blood corpuscles that float in the plasma. 
About five million red corpuscles and ten thousand white 
corpuscles are found in a drop of blood. There are, there* 


THE CIRCULATORY SYSTEM 


14 7 

fore, about five hundred red corpuscles to one white cor¬ 
puscle. 

The Plasma. The blood plasma is composed mainly of 
water. Dissolved in the plasma are the different foods, salts, 
and other materials used by the cells. 

The function of the plasma is to carry 
foods and zvastes, and to form a 
liquid in which the corpuscles can float 
about in the blood vessels. 

The White Corpuscles. The white 
corpuscles can change their shape. 

They are the only cells of the body, 
except the muscle cells, that have 
the power of movement, 1 and more 
than any other of our cells they re¬ 
semble the little one-celled animals about which we studied in 
the first chapter. They often escape from the capillaries 
by passing through between the cells of the capillary wall 
(Fig. 73). For a long time it was thought that the white 
corpuscles had no definite work to do, but roamed about 
while the other cells were busy, each at its particular 
task. Now it is known that the function of the zvhite cor¬ 
puscles is to kill the disease germs which get into the body 
among the cells (Fig. 137). 

The Red Corpuscles. The red corpuscles are small, cir¬ 
cular disks with a hollow in each side, as you see in Figure 72. 
Most of them are formed in the marrow of the spongy bone 
(page 42). Here some of the cells lose their nuclei, take 
on the shape of corpuscles, and by and by float away in 
the blood stream as red corpuscles. For some time they 
circulate through the blood vessels, but finally die and 

1 On ciliated cells (Fig. 6) the cilia move, but the cells as a whole do not. 



Fig. 72. Red and white blood 
corpuscles. 


148 


HUMAN PHYSIOLOGY 


are broken up, chiefly in the spleen. Part of the broken 
down materials of the red corpuscles leave 
the body as the coloring matter of the 
bile. It is estimated that every day 
about fourteen billions of red corpuscles 
die in the body, and as many new ones 
are formed. 

The Function of the Red Corpuscles. 

The function of the red corpuscles is to 
carry oxygen and to assist the plasma in 
carrying carbon dioxid. The way in which 
the red corpuscles carry oxygen is very 
interesting. They have within them a 
substance called hemoglobin . When this 
is exposed to oxygen, as ft is in the lungs, 
each molecule of the hemoglobin unites 
with a molecule of oxygen and carries the 
oxygen away with it. Then, when the 
corpuscle goes out in the capillaries among 
the cells, the hemoglobin 1 gives up its oxy¬ 
gen to the cells (Fig. 74). 

The carbon dioxid is dissolved in both 
the plasma and the corpuscles. It does 
not, however, unite to any extent with the 

fig. 73. A white cor- hemoglobin of the corpuscles, as the oxy- 
puscle escaping from a J 

capillary. gen does, and a corpuscle can carry both 


1 The way the oxygen is carried in the blood may be represented by compar¬ 
ing the blood to a stream, the red corpuscles to little boats in the stream, and 
the hemoglobin molecules to little jars in the boat. In the lungs a molecule of 
oxygen is placed in each of the jars ; out in the capillaries of the body the 
oxygen is emptied out of the jars, and the little boat floats around to the lungs, 
where each jar is again loaded with a molecule of oxygen. 











THE CIRCULATORY SYSTEM 


149 


carbon dioxid and oxygen at the same time. 1 The carbon 
dioxid injures the cells because it is itself poisonous, and 
not by keeping the corpuscles from carrying oxygen to 
them. 

The Color of the Blood. Blood containing oxygen is bright 
red in color, and blood without oxygen is dark, appearing 
blue in the veins under the skin. This you can see by look¬ 
ing at the veins in your forearm, which bring the blood from 
the hand back to the heart. The blood gets its oxygen in the 
lungs (Fig. 81) and loses it in the capillaries of the body. The 
blood is therefore red in the pulmonary veins, in the left side 
of the heart, and in the aorta and all its branches. It is 
dark in the veins bringing the blood from the body to the 
heart, in the right side of the heart, and in the pulmonary 
artery. The same thing can be said more briefly thus: The 
blood is red while going from the lungs to the body capil¬ 
laries, and dark while going to the lungs from the body 
capillaries. 

The Lymph. The blood plasma soaks through the thin 
walls of the capillaries and passes out among the body cells. 
After the plasma gets outside the capillaries it is called 
lymph. The lymph surrounds all the cells in the body and 
fills all the little spaces between the cells. A fresh supply 
of lymph is constantly escaping from the blood, and the 
amount of lymph in the body is several times as great as the 
amount of blood. 

The Function of the Lymph. The function of the lymph is 
to receive food and oxygen from the blood and pass them on to 
the cells , and to receive the wastes from the cells and pass them 

1 In suffocation from gas, death is usually caused by a gas called carbon mon- 
oxid (CO). This unites very firmly with the hemoglobin, and when the blood 
comes to the lungs, the corpuscles cannot take up the oxygen. 


HUMAN PHYSIOLOGY 




150 

to the blood . The cells of the body, except the blood corpus¬ 
cles, lie outside the 
blood capillaries. 
The food and oxy¬ 
gen must pass out 
of the blood capil¬ 
laries before they 
can reach the cells. 
This the food and 
oxygen do by pass¬ 
ing out through the 
capillary walls into 
the lymph, and then 
through the lymph 
to the cells. In 
the same way the wastes reach the blood, passing out of 
the cells into the lymph, and from the 
lymph into the blood. The lymph is 
therefore a middleman between the cells 
and the blood. 

The Cells in the Body surrounded by 
Liquid. Each cell of the body lives in a 
liquid (the lymph) as truly as does a little 
one-celled animal that lives in a pond of 
water. The one-celled animal takes its 
oxygen and food from the water, and its 

J 0 . no. 75. tviusoie 

wastes pass out into the water. The cells ceils and the blood 
of the body take their food and oxygen capillaries that nourish 

from the lymph, and discharge their wastes 

into it. In the pond, however, there is an as are the ceils in Figure 

abundance of food and oxygen for the 74 * 

little animal, and the amount of water in the pond is so great 


FIG. 74. As the blood flows through the capillaries 
it gives food and oxygen to the cells and takes wastes 
from the cells. The lymph acts as a middleman be¬ 
tween the cells and the blood. 






THE CIRCULATORY SYSTEM 


151 


that the wastes have little effect on its purity. In the 
body, on the other hand, the cells are so closely crowded 
that they would in a very short time use all the food and 
oxygen in the lymph, and fill it with poisonous wastes. 
There must therefore be some way of constantly sending into 
the lymph a fresh supply of food and oxygen, and of con¬ 
stantly carrying away the wastes; and this, as we have seen, 
is done by the blood. 


THE LYMPHATIC SYSTEM 

Since the plasma is continually 
escaping from the blood capillaries, 
there must be some way of carrying 
the lymph away from among the 
cells; otherwise too much lymph 
would collect in the tissues and the 
body would become swollen with 
liquid. 1 The lymph cannot go back 
into the blood capillaries against the 
current of escaping plasma, so there 
is another system of vessels (Fig. 78) 
to drain it away from among the 
cells. The vessels that do this are 
called the lymphatic vessels, and their 
function is to collect the lymph from 
among the tissues and carry it again 
to the blood. 

The Lymphatic Vessels. The 

lymph flows into the lymph capil¬ 
laries, which form a thick network 



Fig. 76. A villus and its 
vessels. The lymphatic vessels 
(lacteals) are in black. 


In dropsy the lymph collects in the tissues and causes great swelling. 



52 


HUMAN PHYSIOLOGY 


among the cells. The capillaries unite and form larger 
vessels, which finally empty the lymph back into the blood. 
The lymphatic vessels from the right arm and the upper 
part of the right side of the body empty into a vein in 
the right shoulder (Fig. 66). The lymphatic vessels of the 
remainder of the body empty into the thoracic duct. This 



Fig. 77. A lymph node. The lymph filters through among the white corpuscles in 

the node. 


vessel is about the size of a slate pencil and runs up the 
back of the ventral cavity, bending over at the top, and empty¬ 
ing into a large vein deep in the left shoulder. Thus the 
lymph that escapes from the blood capillaries is taken up by 
the lymphatic vessels and brought back to the blood. 

The Lymphatics of the Small Intestine. Besides taking 
up the escaped plasma from among the cells, the lymphatic 
vessels 1 in the small intestine do another work. The digested 
foods — sugars, proteids, and fats — all pass through the 
walls of the villi (page 93), but to get into the blood the fats 


1 The lymphatics of the small intestine are called lacteals. 





THE CIRCULATORY SYSTEM 


S3 



travel a different road from the others. The sugars and 
proteids pass into the blood capillaries of the villi (Fig. 76). 
The fat enters the lymph capillaries , and is carried to the 
thoracic duct, which empties it into the blood. 

The Lymph Nodes. Scattered through the body are many 1 
white bodies, called lymph nodes . The largest of them are 
perhaps as large as an ordinary 
sized marble, though somewhat 
flattened. If you should examine 
a lymph node, you would find that 


it has a connective-tissue coat and that 
it is filled with white corpuscles. The 
lymphatic vessels pour the lymph into 
these nodes, where it filters through Fig> 78 . The lymphatic 
among the corpuscles in the node much vessels and nodes of a part of 
as water filters through sand grains. thebod y- 
After passing through the node, the lymph is taken up 
and carried on by other lymphatic vessels. The lymph 
from many parts of the body passes through several nodes 
before it reaches the blood. 

The Function of the Lymph Nodes. The lymph nodes have 
two functions : they furnish breeding places for the zvhite cor¬ 
puscles , and they filter out disease germs that get in among the 
cells and are taken up by the lymphatic capillaries. 


1 There are six or seven hundred lymphatic glands in the body large enough to^ 
be seen without a microscope (Fig. 66). 










154 


HUMAN- PHYSIOLOGY 


The white corpuscles that escape from the blood enter the 
lymphatic capillaries and are carried to the lymph nodes. 
Inside the nodes they divide and form new corpuscles. The 
corpuscles reach the blood again by passing into the vessels 
that flow from the nodes and floating in the lymph to the 
blood. 

Many diseases are caused by germs that live and grow 
among the cells. Some of these germs are taken up by the 
lymph capillaries and carried into the lymph nodes. The 
nodes stop the germs, and the corpuscles in the nodes kill 
them. Thus the germs are kept from getting into the 
blood and being carried all through the body. 1 

HYGIENE 

The heart is a muscle, and it is by far the hardest worked 
of all the muscles of the body. It is especially hard-worked 
at that period in life when growth is very rapid, — when a 
boy or girl, in a single year, becomes almost as large as a 
man or a woman. Any extra strain put upon the heart at 
this time is very likely to cause trouble. The heart also be¬ 
comes weak in old age, and old persons should take care not 
to overwork their hearts. The following are the chief causes 
of injury to the heart: 

Severe Exercise. Exercise of the muscles greatly increases 
the work of the heart. Hard work causes any muscle to en¬ 
large, and the extra work thrown on the heart by severe 
exercise may cause “ athletic heart.” In this condition the 

1 In cancer, “ cancer cells ” are carried into the lymph nodes that receive the 
lymph from the diseased tissue, and set up their growth there. It is impossible 
to treat the disease successfully after the cancer cells have reached the lymph 
nodes that lie deep in the body. It is important, therefore, that a physician be 
consulted at the earliest possible moment. 


THE CIRCULATORY SYSTEM 


155 


heart is enlarged, sometimes to several times its natural size. 
This enlarging of the heart is frequently followed by a re¬ 
laxation of the heart and of the arterial walls. The openings 
where the valves are placed are enlarged until the valves 
do not completely close them. The valves then leak and part 
of the blood flows backward in the circulation. This blood 
must be pumped twice, so the work of the heart is in¬ 
creased. Very hard work may also cause fatty degeneration 
of the heart. 

Boys often injure their hearts by bicycle riding. Football 
sometimes injures the heart, requiring too long-continued and 
too severe exercise for any but those with naturally strong 
hearts. Too much playing of tennis may also overtax the 
heart, and any other severe and long-continued exercise may 
do the same. It is well to keep in mind that the time of 
life when the heart is most frequently injured is in youth. 

Headache Remedies. A great number of headache reme¬ 
dies are manufactured from coal tar. They are powerful 
depressors of the heart, and many people have injured their 
hearts with them. They are useful rhedicines, but very dan¬ 
gerous to take except under the advice of a physician. 

Alcohol. The effects of alcohol on the heart and blood 
vessels are very serious. It sometimes causes a paralysis of 
the muscles in the small vessels, so that they are always dis¬ 
tended with blood, as you may have seen in the face and 
eyes of one who uses alcohol excessively. It weakens the 
arteries by causing a fatty degeneration and a hardening 
of the arterial walls. Apoplexy (the bursting of a blood 
vessel in the brain) is therefore more frequent among alco¬ 
holics than among abstainers from alcohol. Alcohol also 
sometimes causes great quantities of fat to be deposited upon 
the heart, thus interfering with its work; it so affects the 


£56 


HUMAN PHYSIOLOGY 


nervous control of the heart that the action of the whole 
organ is weakened. 

The use of alcohol also overworks the heart. It takes 
more force to pump the blood out of the heart into hard, stiff- 
walled vessels than is required to pump it into vessels with 
elastic walls. The work of the heart is therefore increased 
when the arterial walls are hardened by the use of alcohol. 
This, like hard exercise, overworks the heart, and brings on 
enlargement of the heart, trouble with the valves, and fatty 
degeneration. Beer drinkers in particular suffer from heart 
disease, because in addition to enduring all the evil 
effects of alcohol, a beer drinker’s heart is required to 
pump through the system the great quantities of water 
taken in the beer. 

Of course, from reading the above you are not to understand 
that every one who takes alcohol into his body must have all 
these diseases of the heart. You are to understand, however, 
that the effects of alcohol on the heart are bad, and that heart 
disease is much more common among those who use alcohol 
than among those who abstain from alcohol. With such an 
important organ as the heart, no one can afford to take the 
chance of weakening it in any way, for even though in health 
it may seem to be doing its work without difficulty, in an 
attack of pneumonia or other severe illness, when everything 
depends on the heart’s holding out for a few days longer, it 
may suddenly fail. Statistics from a Munich hospital show 
that 16 per cent of all deaths in the hospital were due to 
“beer drinker’s heart,” the weakened hearts failing under the 
strain of disease. 

Tobacco . Tobacco so affects the heart nerves that the 
action of the heart becomes unsteady,— sometimes beating 
very hard and fast, and sometimes with a weak, fluttering 


THE CIRCULATORY SYSTEM 


157 

beat. This trouble is known as “ tobacco heart,” and is very 
common among young cigarette smokers. 

Summary. The body cannot live without the circulation 
of the blood, because it is the blood that carries the food, 
oxygen, and water to the cells, takes away the wastes from 
the cells, and distributes the body heat. 

The blood is pumped through the body by the heart. It 
leaves the heart through the arteries, passes through the 
capillaries, and comes back to the heart through the veins. 
As it passes through the capillaries it gives food and oxygen 
to the cells and takes up the cell wastes. 

The blood is composed of corpuscles and plasma. The 
* plasma escapes through the capillary walls and passes out 
among the cells. It is then called lymph. The lymph is 
taken up by the lymphatic vessels and returned to the 
blood. 

The heart is sometimes injured by too severe exercise, 
headache remedies, alcohol, and tobacco. 


QUESTIONS 

Give three great laws according to which the body lives. What is 
the function of the blood? Explain why the circulation of the blood 
is necessary. 

What are the circulatory organs? Locate and describe the heart. 
Of what are the walls of the heart composed? How many cavities 
are in the heart, and what are they called? Why are the walls of 
the ventricles thicker than the walls of the auricles? What is the 
function of the heart? 

Describe a contraction of the heart. What is the average rate of 
the heart beat ? How fast does your own heart beat? 

Where are the valves in the heart? What is their function? 


<58 


HUMAN PHYSIOLOGY 


Describe the way the valves in the heart close the openings between 
the auricles and the ventricles; the way they close the openings 
from the arteries into the heart. 

What is an artery? a vein? a capillary? How does the blood 
flow in each of these vessels ? How does it get from the arteries 
into the veins ? 

How do the walls of arteries, veins, and capillaries differ? How 
is the size of the opening in an artery changed ? What advantage 
is this to the body? 

Trace the course of the blood from right auricle to right auricle. 
How long does it take the blood to make this circuit ? 

What two kinds of nerves are connected with the heart? with 
the arteries? What proof can you give that the blood vessels are 
controlled by the nervous system? 

How much of the body weight is blood ? Of what is blood com¬ 
posed? What is the liquid part of the blood called? What two 
kinds of corpuscles are in the blood? How abundant are the red 
corpuscles? the white? 

What is the function of the plasma? Where are the white cor¬ 
puscles formed (page 153)? Explain how they escape from the 
capillaries. What is the function of the white corpuscles? 

What shape has a red corpuscle ? Where are the red corpuscles 
formed? What becomes of them? What is their function? What 
substance in them carries the oxygen? Explain how it does this. 
How is carbon dioxid carried in the blood? Why is carbon dioxid 
injurious to the cells? 

Where in the body is the blood red ? Where is it dark ? What 
is lymph? What is the function of lymph? How does the life of 
one of the body cells resemble the life of a small animal in a pond of 
water ? 

What is the function of the lymphatic vessels? Where do the 
vessels from the upper part of the right side of the body empty into 
the blood? What vessel drains the lymph from the remainder of the 
body? Where does this vessel empty into the blood? How do 


THE CIRCULATORY SYSTEM 


I 59 


the absorbed sugar and proteids reach the blood? How do the 
absorbed fats reach the blood? 

Describe a lymph node. How is the lymph carried into and 
through it? What two functions have the lymph nodes? 

At what times of life is the heart especially likely to be injured? 
Why does too severe exercise hurt the heart? In enlargement of 
the heart, what trouble is there with the valves? What effect has 
this on the amount of work the heart must do? Name some of the 
forms of exercise that are likely to injure the heart. 

What effect have headache remedies on the heart? What effect 
has alcohol on the small vessels? on the walls of the arteries? 
What does this sometimes cause? What does alcohol cause to be 
deposited about the heart? How does alcohol increase the work of 
the heart? What additional work.does a beer drinker’s heart have? 
Why is it unsafe to risk injuring the heart ? What per cent of deaths 
in a Munich hospital were due to beer drinker’s heart ? What is the 
effect of tobacco on the heart? 


Press on a vein in your wrist with one finger. On the side of the 
finger toward the heart empty the vein by rubbing another finger 
along it. Does the blood flow back into the vein ? On the other side 
of the finger that is pressing the vein, rub the blood away from the 
heart. Does the blood flow back into the vein? Explain. 

Explain why a steady stream of water comes out of the end of a 
long rubber hose into which water is being pumped with intermittent 
strokes. The blood in the arteries flows in spurts, and in the capilla¬ 
ries and veins it flows in a steady stream. Explain why it does this. 
Why does it require more force to pump water into an iron pipe than 
into a rubber hose with elastic walls? 

Does a wave on a river travel with the same speed as the water in 
the river? Do the blood and the wave in the blood that causes the 
pulse in an artery, travel with the same speed ? 



CHAPTER XII 


RESPIRATION 

Watch the chest of some one who is near you, and you 
will see that it alternately rises and falls. As the chest 
rises, air is taken into the lungs. This is called inspiration. * 
When the chest falls, the air is driven out of the lungs. 
This is expiration. The whole process of taking the air into 
the lungs and sending it out of them is called breathing, or 
respiration. Like the circulation of the blood, respiration 
goes on night and day as long as the body lives. 

The Object of Respiration. The object of respiration is to 
take oxygen into the body and to give off carbon dioxid from the 
body. When the blood passes through 
the lungs, it takes up a new oxygen sup¬ 
ply for the cells, and loses the carbon 
dioxid which it has carried away from the 
cells. Without respiration, the circulation 
of the blood would be useless, for the 
blood could not obtain oxygen, and it 
would carry through the body again and 
again the poisonous carbon dioxid which 
it takes up from the cells. 
fig. 79 . Burning low for Why Oxygen is Necessary to the Cells. 

lack of oxygen. When the foods are oxidized (burned) 

within the cells, the atoms of the foods unite with atoms of 
oxygen. By this process, energy is given to the cells (page 

160 






RESP/RATION 


l6l 

114). If there are no oxygen atoms in the cells for the food 
atoms to unite with, it is evident that the oxidation of the 
foods within the cells must come to a stop. The cells will 
then be unable to get energy, and they will die. Without 
oxygen they cannot use the food, and without oxygen they 
starve to death for lack of energy as surely as if no food had 
reached the cells. Oxygen is necessary that the foods may be 
burned within the cells. As oxygen is necessary for the burn¬ 
ing of the foods within the cells, so it is necessary for the 
burning of all substances everywhere. Cover a candle by set¬ 
ting a glass vessel over it (Fig. 79). In a few moments the 
candle will go out because there is no more oxygen in the 
vessel. 

THE ORGANS OF RESPIRATION 

The organs of respiration include the framework of the 
chest , the muscles that are used in breathing , the lungs , and 
the air passages. The lungs are the most prominent of these 
organs, and it is in them that the blood gives off its carbon 
•dioxid and takes up its oxygen. Most of the diseases of the 
respiratory organs are caused by germs that grow on the 
warm, moist lining of the air passages, and in the air sacs of 
the lungs. 

The Lungs. The lungs (Fig. 84) are composed chiefly of 
a great mass of air passages and air sacs. They therefore 
have a light and spongy structure. In the lungs blood ves¬ 
sels are very abundant, for at each beat of the heart as much 
blood goes to them as goes to all the remainder of the body. 
The lungs are hung in the thoracic cavity by the trachea 
(Fig. 82), through which air passes into and out of them. 
Each lung is surrounded with a thin connective tissue sac 
called a pleura (plural, plenrce). 


HUMAN PHYSIOLOGY 


162 


The Thoracic Cavity. 



Fig. 80. The divisions of the 
thoracic cavity. 


The thoracic cavity (Fig. 8) lies 
within the framework of the chest, 
and the diaphragm 1 forms its floor. 
It is divided longitudinally into three 
chambers (Fig. 80). In each side 
chamber lies a lung. In the central 
chamber the heart and the bases of 
the great blood vessels, the trachea, 
and the esophagus are found. The 
central chamber is wider in its lower 
front portion where the heart lies, and 
narrower above and behind the heart. 
The pleura are two 

l 


The Pleurae. 

thin, double-walled sacs. The outer 
layer of a pleura is attached to 
the chest wall and diaphragm, and 
stretches as a partition across the 
thoracic cavity from top to bottom. 

The inner layer incloses the lung. 

This layer of the pleura is very 

delicate, and forms a thin coat over '-wall of ** sac 

Fig. 81. Air sacs and blood 
the Surface of the lung. In Figure vessels in the lungs. The blood 
80 you can see how the chest capillaries lie in the thin walls 

cavity is divided into three parts passes through the capil]aries 
by the pleurae, and in Figure 82 carbon dioxid and water pass 
you can trace a pleura entirely out into the air sac> and oxy ‘ 

. . . , J . gen passes from the sac into the 

around a lung and around the blood. 



1 The diaphragm (Fig. 8) is a thin sheet of muscle with a connective tissue 
center. It is dome-shaped, the stomach and liver fitting into the hollow in its 
lower surface. Viewed from above, the diaphragm appears as a ring of muscle 
7 vith a connective tissue center. It is attached all around by its outer edge to the 
body wall, specially heavy bands of muscles running down and attaching them- 




RESP/RA T/OJV 


163 

cavity in which the lung lies. 1 The surfaces of the pleurae 
are kept moist with a thin yellowish liquid. 2 This prevents 
friction when the two layers of the pleura move on each 
other in breathing. 



How the Chest is enlarged in Inspiration. In inspiration 

the chest is enlarged in two ways. The ribs and sternum ai'e 
lifted up and out , widening the cavity of the chest. The dia¬ 
phragm is drawn downward , causing the bottom of the chest 
cavity to sink, and thus increasing the size of the cavity. The 

selves to the front of the spinal column. When the muscles of the diaphragm 
contract and shorten, they draw its top (center) downward. 

1 The pupil should also trace out the course of the pericardium and note 
that it is a double-walled sac enveloping the heart as a pleura envelops a lung. 

2 The disease called pleurisy is inflammation of the pleurae. In this disease 
considerable quantities of liquid may collect between the two layers of the pleurae 










HUM AIV PHYSIOLOGY 


164 


chest walls and the diaphragm are thus drawn away from the 
lungs, leaving a vacuum , or empty space, between the two 
layers of the pleurae. The air then rushes down into the lungs, 
and expands them until they fill the enlarged thoracic cavity. 
So promptly do. the lungs expand and follow up the chest 
walls and diaphragm in inspiration that there is no noticeable 
space between the two layers of the pleurae. 

Expiration. In ordinary expiration, the muscles do little 
work. The ribs and sternum sink chiefly from their own 
weight, and the diaphragm is pushed 1 up by the liver, stomach, 
and other abdominal organs below it. This with the elasticity 
of the lungs drives out the air; for just as the stretched walls 
of a blown-up football or of a toy balloon expel the air, so the 
stretched walls of the air sacs and of the small bronchial tubes 
help to force the air out of the lungs. 

The Nasal Passages and the Pharynx. When air is taken 
into the lungs, it first enters the nasal passages (Fig. 83). 
These are two narrow chambers that run up in the head as 
high as the eyes and backward about four inches. An open¬ 
ing in the floor of each nasal chamber at the back leads down 
into the pharynx. 

The pharynx is a funnel-shaped cavity lying behind the 
mouth. It curves around the base of the tongue, with its 
mouth opening forward. Hanging down in front of the 
openings from the nasal chambers and helping to separate the 
mouth from the pharynx is a little curtain-like structure called 

1 When the diaphragm comes down in inspiration, it forces the organs below it 
downward anrl pushes the abdominal walls outward. In expiration the stretched 
abdominal walls come inward partly because of their elasticity, and partly because 
of the contraction of the abdominal muscles, and drive the diaphragm upward. 
In a forced expiration, the abdominal muscles contract forcibly, pulling in the ab¬ 
dominal walls and driving the diaphragm far upward. At the same time they 
draw down the ribs and sternum, to which they are attached at their upper ends. 


RESPIRATION 


65 


the uvula , or soft palate. In swallowing, the uvula is pushed 
back over the openings from the nose so that it covers them 
and prevents food and water from entering the nose (Fig. 83). 

In the side walls of the pharynx, directly under the corners 
of the lower jawbone, the two tonsils 1 are located. When 
viewed from the inside of the pharynx, the tonsils appear 
like gentle, rounding elevations lying under the mucous mem¬ 
brane which lines the pharynx walls. At the bottom of the 
pharynx are two openings, one leading into the esophagus 
and one into the larynx. 

The Larynx. The larynx is the enlarged upper part of 
the trachea. It has a framework of cartilages, which you 
can easily feel in the front of your neck. In swallowing, the 
food and drink would fall down into the larynx if it were not 
for the epiglottis (Fig. 83). This flap-like structure stands 
in front of and above the opening to the larynx, and in swal¬ 
lowing the larynx is drawn up and forward, 2 so that its mouth 
is pushed up in under the epiglottis. The food or water 
then passes over the larynx into the esophagus. During 
breathing the larynx drops down, leaving its mouth open, and 
allowing the air to pass into and out of the lungs. The vocal 
cords , which produce the sound of the voice, are in the larynx. 

The Trachea and its Branches. The trachea divides into 
two great branches, one of which goes to each lung. Within 
the lung these branches divide again and again, until finally 
they end in little air sacs. The branches of the trachea are 

1 When germs get into the tonsils and cause inflammation, the disease is called 
tonsilitis. 

2 Feel your larynx while you swallow, and note how it rises. If one laughs 
when eating or drinking, the larynx is lowered and food or water may fall down 
into the trachea. When food or liquid is driven upward through the pharynx in 
laughing or by vomiting, it may pass in behind the uvula and enter the nasal pas¬ 
sages from the rear. 


HUM A AT PHYSIOLOGY 


166 


SPINAL CANAL 


called the bronchial tubes. In the walls of the trachea and 
of all the larger bronchial tubes are rings of cartilage to keep 

the air passages from 
closing and shutting 
off the supply of air 1 
from the air sacs in 
the lungs. 

The Air Sacs. Each 
small bronchial tube 
at the end widens out 
and becomes a thin- 
walled sac. The walls 
of this sac are thrown 
into little sac-like 
folds, so that the end 
of a bronchial tube is 
a larger sac 2 made up 
of a great number of 
little sacs, all opening 
inward toward the 
center. So abundant 
are the air sacs in the lungs that their estimated number is 
725,000,000, and if they were all opened and spread out side 
by side, they would cover 2150 square feet of space. 

Changes in the Air in the Air Sacs. The walls of the air 
sacs are exceedingly thin. They contain a very great 



Fig. 83. The air follows the path indicated by 
the blue arrows, and the food follows the path indi¬ 
cated by the red arrows. 


1 In asthma the muscles in the walls of the small bronchial tubes contract so 
that the greatest difficulty is experienced in getting the air to pass in and out of 
the air sacs. In pneumonia the small air passages and the air sacs are stopped 
up with mucus. 

2 The larger air sacs at the ends of the bronchial tubes are called infundibula 
(singular, infundibulum ). The smaller air sacs of which an infundibulum is 
composed are called alveoli (singular, alveolus). 






RESPIRATION 


167 


number of delicate blood' capillaries through which all the 
blood in the body passes every minute and a quarter (page 
145). As the blood flows through the capillaries in the walls 
of the air sacs, oxygen from the air passes in through the 
walls of the sacs and enters the blood, and carbon dioxid 



FIG. 84. The trachea and the lungs. B and C show the way the small bronchial 
tubes end in air sacs ( infundibula ) which are made up of a large number of smaller sacs. 


passes out from the blood into the air (Fig. 81). Water also 
passes out of the blood into the air, as you can prove by 
breathing on a cold window pane, and the air is warmed 
while in the lungs. The air in the lungs, therefore, loses 
oxygen, and gains carbon dioxid, water, and heat. 

Perhaps what is going on in the lungs would be made more vivid 
to you, if, in imagination, you could make a trip down into the lungs 
and see what is happening there. Following down the trachea and 
the bronchial tubes, you would come into one of the larger air sacs. 






HUMAN PHYSIOLOGY 


168 

There you would see all about you the mouths of the little air sacs 
opening into the chamber in which you were standing. Going up to 
the mouth of a small sac and looking in, you would see the blood 
shooting along in the capillaries in the walls. As the blood enters 
the capillaries, it is dark in color, but as it moves along it gradually 
takes on a redder and redder hue until it is a bright scarlet when it 
gets through the capillaries and starts to the heart. 

Peering still more closely into the sac, you would see a great mul¬ 
titude of little oxygen molecules flying from the air into the blood, 
where they unite with the hemoglobin of the red corpuscles and are 
carried away. You would also see the carbon dioxid and water 
molecules flying out from the blood into the air in the little sac, and 
then passing out into the larger sac and up into the bronchial tubes, 
to pass out of the lungs in the breath. 

Mucus and Cilia. The entire respiratory tract is lined with 
mucous membrane and is kept moist with sticky mucus. 
In all parts of it except in the pharynx and air sacs and over 
the vocal cords, the walls are covered with cilia (Fig. 6). 

The mucus on the walls of the air passages catches dust 
and germs that are in the air, and the cilia sweep the mucus 
and matter which is caught in the mucus out of the air pas¬ 
sages. The air is thus cleansed, and irritating dust particles 
and dangerous disease germs are in a great measure prevented 
from getting down into the delicate air sacs of the lungs. 

The nasal passages are especially fitted for purifying and 
warming the inhaled air. The nostrils are guarded by hairs 
for straining out dust, the mucus on the walls of the long and 
narrow nasal passages catches much dust and many germs, 
and air inhaled through the nose is warmed before it reaches 
the throat and lungs. Any trouble in the nasal passages 1 


1 Nasal polyps close the passage through the nose, and adenoids (spongy 
growths above and behind the uvula) block the openings from the nose to the 
throat. The teacher should report to the parents all children who have trouble 
in breathing through the nose (pages 253, 270). 


RESPIRATION 


169 


that interferes with breathing through the nose should 
receive medical attention at once, for in mouth breathing, 
cold and dusty air is taken into the throat and lungs. This 
brings on many diseases of those parts. 

RESPIRATION IN OTHER ANIMALS 

An insect has no lungs, but it takes in air through a great 
number of little tracheae, or air tubes, which open along the 
sides of its body. A fish has very thin gills through which 
the blood flows. The fish takes water into its mouth and 
sends it backward over the gills and out through the gill slits 
on the sides of its neck. As the water passes over the gills, 
the oxygen from the water passes into the blood, and the 
carbon dioxid from the blood is given off into the water. 
A fish cannot live in boiled water, because when water is 
boiled, the air is driven out. It cannot live in the air, 
because when taken out of the water, its gills stick together, 
and the oxygen cannot get in among the gills to pass into 
the blood. 

The frog, instead of making a vacuum in his chest and thus 
causing the air to pass into the lungs, takes air into the mouth, 
and by drawing in the skin under its chin, forces the air 
downward. Watch a frog breathing, and note how the throat 
works out and in. When under water, the frog breathes by 
absorbing oxygen through its thin, moist skin. It may inter¬ 
est you to know that a frog does not drink water, but absorbs 
this also through the skin, the water passing into the blood 
which flows in the capillaries of the skin. 

A bird has no diaphragm and the lungs run far back in the 
body. In many birds branches from the lungs go out even 
into the hollow bones. 


70 


HUMAN 1 PHYSIOLOGY 


HYGIENE 

Five points connected with the hygiene of the respiratory 
system are worthy of notice. The first is in regard to the 
effects of tight clothing about the body. This interferes with 
the respiratory movements, and is a great evil, for it leads to 
shallow breathing, in which the air passes into and out of the 
trachea and larger bronchial tubes without sending much oxy¬ 
gen into the air sacs or taking much carbon dioxid out of them. 

The second point is in regard to the danger of breathing 
dust. Large numbers of people die every year from consump¬ 
tion, pneumonia, diphtheria, and grip, and many more suffer 
from catarrh and other diseases of the respiratory organs. 

Practically all of these diseases are caused by germs that are 
inhaled in the air. Many people have the idea that these 
germs are floating around singly in the air, but this is a mis¬ 
take. They are sticking to dust particles, small pieces of lint 
from cloth, and other little particles of matter that are in the air. 
Every effort should be made, therefore, to keep from breathing 
dust. Streets should be kept sprinkled, and when floors are 
swept, as little dust as possible should be raised. Dust should 
be wiped from walls and furniture with a damp cloth, and not 
stirred up into the air. Everything possible should be done to 
prevent the inhalation of dust, for most respiratory diseases 
are germ diseases, and the germs are frequently carried into 
the nose, throat, and lungs by dust. 

The third point which we wish to mention is the value of 
deep breathing exercises} It is an excellent plan for every 
one, several times a day, to stand erect, as directed on page 
7 1, fill his lungs to their utmost capacity, hold the air for a 

1 It is well to know that breathing exercises are very injurious to any one who 
is suffering from consumption. 


RESPIRATION 


171 


few moments, and then slowly and steadily exhale it. This 
takes the oxygen deep into the lungs, brings out the carbon 
dioxid, and quickens the heart beat, thus starting the blood 
more swiftly through the whole body. 

Outdoors, in the fresh air, is the best place to take these 
breathing exercises, and you can practice them as you walk 
to and from school. But a better time to practice them is 
when you have' become tired from sitting over some task for 
a considerable time. Then you will find that it will rest and 
refresh you to go to a window, open it, and take several deep 
breaths of fresh air. In school, when every one has been 
sitting quietly until the respiration has become shallow and 
the heart beat slow, it is very beneficial to throw the win¬ 
dows wide open and have everybody stand up and take 
several deep breaths, along with some stretching exercises 
to relieve the cramped muscles. A couple of minutes spent 
in this way takes very little time, and sets everybody to work 
again with renewed vigor. You must take care, however, not 
to practice breathing exercises so vigorously that you make 
yourself dizzy, or you may do yourself more harm than good. 

The fourth point to which we would call your attention is in 
regard to the use of alcohol. Users of alcohol are particularly 
liable to attacks of pneumonia, catarrh of the pharynx, larynx, 
and bronchial tubes, and to other respiratory diseases. The 
chief reason for this seems to be that alcohol weakens the power 
of the body to kill germs. We shall take up this whole subject 
in a later chapter, but you should know now that when pneu¬ 
monia or grip is abroad, and every one is trying to keep himself 
in the best possible health so that he will be able to kill any germs 
that get into his body, drinking alcohol, even in small amounts, 
will greatly lessen the power of the body to resist germs. 

The last point which we would ask you to note in connec- 


172 


HUMAN PHYSIOLOGY 


tion with the hygiene of the respiratory organs is the effect of 
cigarette smoking on the lungs and on the health of the whole 
body. Users of cigarettes very commonly inhale the smoke. 
This smoke is irritating to the air passages and has a very 
injurious effect on the lungs. In addition to the poisonous 
substance that is in the tobacco, cigarette smoke contains a gas 
called carbon monoxid (page 149, footnote). Both the poison 
of the tobacco and the carbon monoxid pass into the blood in 
the capillaries of the lungs and injure the cells of the body. 


THE VOICE 


The Cartilages of the Larynx. 




Fig. 85. The cartilages of the larynx. 
A and B show the cartilages as seen from the 
front. C is the back of the cartilages in their 
natural position. D is a longitudinal section 
of the larynx showing the vocal cord stretched 
from the thyroid cartilage in front to the vocal 
process of the arytenoid cartilage at the back. 


The walls of the larynx are 
mainly composed of two 
great cartilages, the thyroid 
and the cricoid. The thyroid 
cartilage is the “Adam’s ap¬ 
ple” which you can feel in 
the front of your throat. It is 
somewhat V-shaped, with the 
opening behind. Set upon 
end a partially opened book, 
and it will represent fairly 
well the shape of the thyroid 
cartilage. 

The cricoid cartilage forms 
a complete ring, but it is much 
narrower in front than be¬ 
hind (Fig. 85 B). In front, 
the cricoid lies in the larynx 
wall below the thyroid (Fig. 
85 D) } but at the back its 







RESPIRATION 


73 


wide part stands up between the two wings of the thyroid 
and forms the back wall of the larynx (Fig. 85 C). 

On top of the cricoid, at the back, stand up the two little 
arytenoid cartilages. Each one is loosely hinged at its base, 
so that to a certain extent it can slide outward toward the side 
wall of the larynx or inward toward the other arytenoid. It 
has on the inner side of the base a small projection called 
the vocal process (Fig. 85 B ), to which the back end of the 
vocal cord is attached. 

The Vocal Cords. The vocal cords are insignificant little 
bands of connective tissue that run along the side walls of 



Fig. 86. The mouth of the larynx viewed from above. A shows the position of 
the vocal cords ( c ) in deep breathing; B is their position in ordinary breathing; and C 
shows them brought together for speaking or singing, a is the epiglottis. 


the larynx from the front to the back. They are attached 
to the thyroid cartilage in front and to the vocal processes 
of the arytenoid cartilages at the back. They are buried in 
the mucous membrane that lines the larynx, and are therefore 
attached to the side wall of the larynx by one edge. If you 
will gather up and draw out a fold of skin on the back of the 
hand, you will have something that in a way represents a 
vocal cord. 

The Vocal Cords in Action. In ordinary breathing the vocal 
cords lie close to the walls of the larynx and are not affected 
by the air as it passes out of and into the lungs. In talking 
or singing the cords are drawn out from the walls and stretched 


174 


HUMAN PHYSIOLOGY 


across the opening of the larynx, until there is only a narrow 
slit between the cords. The air passing out over the tightly 
stretched cords causes them to vibrate and produce the sound 
of the voice. To make a gentle sound, a slight current of 
air is passed over the vocal cords. To make a loud sound a 
heavy current of air is sent out. 

How the Vocal Cords are thrown into and out of Action. 
The vocal cords are thrown into and out of action by mus- 




Fig. 67. Diagram illustrating how the vocal cords are brought into action. When 
the points of the arytenoid cartilages (represented by the gates in the diagram) to which 
the cords are attached are turned forward, the cords lie close to the wall. When the 
cartilages s\v ing out, as in D, the cords are drawn out from the walls, as in C. 


cles that are attached to the arytenoid cartilages. When a 
sound is to be produced, the arytenoid cartilages are made 
to slide inward toward each other and are rotated (Fig. 87 D), 
so that they draw the vocal cords out from the walls (Fig. 
87 C). The cords are thrown out of action by sliding the 
arytenoid cartilages outward and rotating them so that the 
vocal processes point forward (Fig. 87 B). This allows the 
cords to lie close to the larynx walls (Fig. 87 A). 

The Pitch of the Voice. The heavy strings of a guitar or 
of a violin give a low tone, and the light strings give a high 
tone. In strings of the same weight, a tight string gives a 





















RESPIRATION’ 


r 75 

higher tone than a loose string, and a short string a higher 
tone than a long string, as you can tell by tightening the 
strings on a stringed instrument, and changing their lengths 
by fingering them. The pitch of the sound depends, there* 
fore, on the weight , the length , and the tightness of the string. 

Persons who have long and heavy vocal cords have low 
voices, and persons with short and light vocal cords have 
high voices. The larynx of a man is larger than the larynx 
of a woman, his vocal cords are larger and longer, and his 
voice has, therefore, a lower pitch. 1 

Change of pitch in the voice is brought about by the mus¬ 
cles of the larynx tightening and loosening the vocal cords. 
When a low tone is to be produced, the cords are loosened. 
When a high tone is to be produced, the cords are tight¬ 
ened. When one thinks how many notes a singer makes 
in a few minutes, tightening the vocal cords just enough to 
give the right pitch to each one, he realizes how rapidly and 
accurately the muscles of the larynx must work. 

Summary. Respiration is necessary to take in oxygen and 
give off carbon dioxid. The lungs are in the thoracic cavity. 
This cavity is enlarged and air drawn into the lungs by 
lifting up the framework of the chest and by pulling down 
the diaphragm. 

The air passes through the nasal passages and pharynx 
enters the larynx, and goes down the trachea and its 
branches into the air sacs of the lungs. In the air sacs it 
gives up its oxygen to the blood and takes up carbon dioxid 
and water from the blood. The air passages are lined with 

1 When male and female voices sing in unison, the male voices are an octave 
lower than the female. At the time when a boy’s voice changes, the larynx sud¬ 
denly grows very much larger, and the vocal cords are lengthened. While the 
voice is changing it should not be given any severe use. 


;6 


HUMAN PHYSIOLOGY 


mucous membrane, and in most parts the walls are covered 
with cilia. The mucus catches dust, and the cilia sweep it 
out of the air passages. 

Tight clothing about the body interferes with breathing; 
many diseases of the respiratory organs come from breathing 
dust; deep breathing exercises are very valuable ; alcohol 
brings on lung diseases; and cigarette smoking injures the lungs. 

The cartilages of the larynx are the thyroid, cricoid, and 
arytenoids. The vocal cords are attached to the thyroid in 
front and to the arytenoids behind. In speaking or singing, 
the vocal cords are thrown out from the wall, and the voice 
is produced by passing a current of air over the cords. The 
pitch of the voice depends on the weight, length, and tight¬ 
ness of the cord’. 


QUESTIONS 

What is inspiration? expiration? respiration? By observing the 
breathing of some person who does not know what you are doing, find 
out how many times he breathes in a minute. 

What is the object of respiration ? Why is oxygen necessary to 
the body? Of what are the lungs chiefly composed? How much 
blood goes to the lungs? What is the covering of a lung called? 
Into how many parts is the thoracic cavity divided? What is in the 
side chambers of the thoracic cavity? the middle chamber? Make a 
drawing showing the location of a pleura. 

In what two ways is the chest enlarged ? How is the air forced 
out of the lungs? Trace the air down into the lungs, naming the 
different parts of the air passages. Describe the nasal passages. 
How does the air get from the nasal chambers into the mouth? 

Describe the pharynx. What separates the pharynx from the 
mouth? What is its use? Where are the tonsils? How are food 
and water kept from falling into the larynx? 

Describe the branching of the trachea. What are the branches of 


RESPIRATION' 


1 77 


the trachea called ? How are the trachea and bronchial tubes kept 
open? Describe an air sac. In what length of time does all the 
blood in the body pass through the lungs? What passes from the air 
into the blood ? from the blood into the air? 

With what is the respiratory tract lined? How is it kept moist? 
What parts of the respiratory tract are covered with cilia? What is 
the use of the mucus? of the cilia? What are the nasal passages 
especially fitted to do? Why is mouth breathing harmful? 

How does an insect breathe ? a fish ? Why cannot a fish live in 
boiled water? in the air? How does the frog take air into its lungs? 
How does it breathe while in the water? How does a frog take 
water into its body? What is peculiar about a bird’s lungs? 

Why is tight clothing harmful? Name five diseases caused by 
breathing in germs from the air. How are germs carried in the 
air? What measures are useful in keeping down dust? 

What effect have deep breathing exercises on the heart beat and 
circulation? Where should such exercises be taken? when? To 
what respiratory diseases are users of alcohol particularly liable? 

Name the two large cartilages in the larynx. Describe the thy¬ 
roid cartilage; the cricoid. Where are the arytenoid cartilages? 
How can they be moved ? Describe the vocal cords. To what are 
they attached at the front? at the back? along the edge? 

What is the position of the vocal cords in ordinary breathing? 
in talking or singing? How is the voice produced? How is a 
gentle sound produced? a loud sound? How are the vocal cords 
thrown into action? out of action? 

Upon what does the pitch of a sound depend? What kind of 
vocal cords have persons with low voices ? persons with high voices ? 
Why has a man’s voice a lower pitch than a woman’s voice? How 
is the pitch of the voice changed? 

When a bucket is lowered in water, what causes the water to rush 
into it? We live at the bottom of an ocean of air. What causes 
the air to be drawn into the lungs when the chest cavity is enlarged? 


CHAPTER XIII 


VENTILATION 

Of all the evils that befell man when he left his forest 
home and came to dwell within walls and doors, the lack of 
fresh air is the greatest. By its own activity, the body is 
constantly manufacturing great quantities of a very poisonous 
gas, — carbon dioxid. As long as man dwelt in the great 
outdoors, all that was necessary was for the body to get this 
gas outside of itself, and the ever moving currents of air 
carried it away where it could not reenter the lungs. But 
within doors, when the lungs have thrown off the carbon 
dioxid, they often find their work of no avail, for the air is 
imprisoned, and the carbon dioxid is breathed again into the 
lungs, reenters the body, and poisons the cells. The cells 
then become weak and diseased, and fail in their work. 
Disease germs creep in, the weakened body cannot kill them, 
and the troubles thus started often end only with the end of 
life. So we say again, that of all the evils that have come to 
civilized man because he dwells within doors, the lack of 
fresh air is the greatest. 

The Air. The air consists of about four fifths nitrogen 
and one fifth oxygen, with small amounts of several other 
gases which vary at different times and places. Among the 
gases that exist in small quantities in the air is carbon dioxid, 
which in ordinary air makes up nearly 4 parts in 10,000. 
The nitrogen is not used in the body, but passes into and out 
of the lungs unchanged. It is the oxygen and the carbon 
dioxid that have an interest for us. 

178 


VENTILATION 


1 79 

The Supply of Oxygen. Twenty-one per cent of the air is 
oxygen. It is absolutely necessary for life, but under ordi¬ 
nary circumstances the air and the blood always contain 
enough oxygen for the cells. As long as more than io per 
cent of the air is oxygen, a person lives as well as if he were 
breathing pure oxygen. Expired air still contains 15 percent 
of oxygen, so there would be no lack of oxygen in the body, 
even though the air were breathed twice. 

Carbon Dioxid. Air contains a little less than 4 parts in 
10,000 of carbon dioxid. Expired air contains about 430 
parts in 10,000 of carbon dioxid. Stating it in another way, 
ordinary air is .04 per cent carbon dioxid, and expired air is 
4.3 per cent carbon dioxid. The air that leaves the lungs, 
therefore, contains more than a hundred times as much car¬ 
bon dioxid as the air that enters them. It is the carbon 
dioxid in the air which is so injurious in crowded and poorly 
ventilated buildings, and to get rid of carbon dioxid is the 
great problem of ventilation. 

Effects of Carbon Dioxid Poisoning . 1 A small amount of 
carbon dioxid in the air causes drowsiness and mental dullness. 
Long-continued exposure to carbon dioxid causes paleness and 
general ill health. Large amounts of carbon dioxid in the 
air cause trembling and weakness, followed by stupor and death 
if the breathing of the gas is prolonged. The “ choke damp ” 
sometimes found in coal 'mines is carbon dioxid, and carbon 
dioxid is sometimes found in dangerous quantities in old wells. 2 

1 It has been thought that there is some injurious substance in expired air 
besides the carbon dioxid, but no such substance has been discovered. The 
headaches that follow breathing the air of crowded rooms are probably not due to 
carbon dioxid, but to overheating, the moisture of the air, and disagreeable odors. 

2 Before descending into a well it is sometimes advisable to learn whether or 
not there is carbon dioxid in the well by lowering a lantern into it. If carbon 
dioxid is present in large quantities, the lantern will go out, Why? 


i So 


HUMAN PHYSIOLOGY 


Amount of Fresh Air needed. To keep the amount of car¬ 
bon dioxid in the air from becoming too great, a man must 
have 3000 cubic feet of fresh air every hour. If he is 
working, he will need twice this amount. An eight-year-old 
boy needs one half as much as a man. 

Usually it is not possible to change the air of a room more 
than five times an hour without causing drafts. Changing it 
five times an hour, each person must have 600 cubic feet of 
air space in a room to get his 3000 cubic feet of fresh air. 
Public buildings, therefore, should have 600 cubic feet of air 
space for each person, and in the living and sleeping rooms 
of private dwellings, each member of the family should have 
1000 cubic feet of space. 1 Of course, even with this much 
space, the air will become bad unless there is some way of 
constantly changing it. 

How to tell when the Air in a Room is Bad. All of us suffer 
more or less from carbon dioxid poisoning, and ventilation is 
probably the most important of all the problems of hygiene. 
It is, therefore, very important for us to be able to tell when 
the air in a room is bad. One fairly good way of doing this 
is by the nose. If the air in a room smells close when one 
comes in from outdoors, the ventilation is not sufficient. 
After staying in a badly ventilated room for a time, the smell 
of bad air is not noticed, but after one has been out in the 
fresh air, the nose is a fairly good judge of the quality of air. 

Principles of Ventilation. A room will hold only a certain 
amount of air, and if fresh air is brought in, part of the air 
already in the room must pass out. In any system of venti- 

1 Lamps and gas jets give off carbon dioxid, and where these are burning, an 
extra supply of air is needed. Oil stoves and gas stoves that are not connected 
with a chimney are exceedingly unhealthful, for they give off large quantities of 
carbon dioxid into the air of the room. 


VENTILATION' 


18 r 


lation there must, therefore, be an opening through which the 
air can enter the room, and an opening through which it can 
escape. The cold air in a room sinks to the floor and the 
warm air rises to the top of the room. The opening by which 
the air is drawn off from the room should, therefore, be near 
the floor. 

In ordinary buildings some air finds its way through crevices 
around windows and doors and through the floors. Opening 
and closing doors, and persons passing in and out of a room, 
also create a circulation of the air. Air may pass both out 
and in through the same opening, as you can show by the 
following experiment: 

Hold a lighted candle near the top of an open doorway. The candle 
flame will be blown to one side, showing that a current of air is passing 
in or out through the top of the doorway. Now hold the candle in the 
doorway close to the floor. The air current here will usually be found 
to be passing in a direction opposite to the direction of the current 
of air in the top of the doorway. By holding the candle at different 
heights, find a stationary layer of air lying between two layers of air 
that are moving in opposite directions. Open or close some other 
door of the room and note the effect on the candle flame. Have 
some one walk through the doorway past the flame and note the 
effect. 

Ventilating Public Buildings. In many public buildings it is 
impossible to have satisfactory ventilation, because the builders 
did not provide any special arrangements for drawing off the 
used air and for sending in a supply of fresh air. Windows 
were put in houses, not to be used as ventilators, but to 
admit light, and it is very difficult to use them as ventilators 
without causing drafts. In schoolhouses, churches, theaters, 
and other buildings, where many people collect, some way of 
forcing in fresh air and of drawing off the air which has 
been used, should be provided. Unless this is done, it is 


182 


HUMAN PHYSIOLOGY 


almost impossible in cold weather to change the air rapidly 
enough to prevent carbon dioxid from accumulating in the 
building. 

Heating Systems and Ventilation. Heating with a hot-air 
furnace is healthful, 1 for a furnace constantly sends a supply 
of fresh air into the room. A fireplace gives considerable 



Fig. 88. How a fireplace helps to ventilate a room. A current of air passes up 
the chimney, and this causes the fresh air to be drawn into the room. 

ventilation by causing a draft of air up the chimney. Stoves 
give some ventilation in the same way, but not so much as an 
open fire. Radiators heated by hot water and steam give 
no ventilation. 

Avoiding Drafts. The great problem connected with venti¬ 
lation is how to get the fresh air into the room without causing 
cold drafts. One of the most satisfactory ways of doing this 
is to have warm air sent in by the heating system. Some 


1 Some cheap iron furnaces, when they become red hot, allow gas from the 
coal to pass through them. Breathing this gas is exceedingly unhealthfuL 
























































VENTILATION' 


183 

very useful devices for ventilating are made, by which air is 
drawn in behind a fireplace or into a jacket around a stove 
and warmed before it comes into 
the room. A board set under a 
window sash allows the air to come 
in between the two sashes and go 
upward without causing a draft on 
those sitting in the room. You can 
still further improve on this kind of 
ventilator by cutting two or three 
holes in the board and boxing them 
in, as shown in Figure 89. 

Even when buildings have been 
constructed with no ventilating sys¬ 
tem, it is possible to do much to 
secure fresh air without causing 
harmful drafts. Several windows 
may each be opened a little, when 
to open one wide would cause great trouble. Schoolrooms 
and churches should be filled with fresh air while they are 
empty. At noon and during recesses schoolroom windows 
can be opened and a great deal done in a very short time 
toward getting out the stale air. 

Importance of ventilating Sleeping Rooms. A great deal 
of time is spent in the atmosphere of the sleeping room, and 
at night the air of sleeping rooms is not set in motion by the 
opening and closing of doors and by persons passing out and 
in. For these reasons the ventilation of the room where you 
sleep deserves special attention. 

If your sleeping room is not ventilated in some other way, 
you should open one or more windows each night. If the 
windows are so arranged that they cannot be opened without 



FlG. 89. Ventilating by placing 
a board under a window. 

























8 4 


HUMAN PHYSIOLOGY 


causing a draft over the bed, fit boards under the sashes, 
or get fresh air in some other way. Do not sleep in a 
closed room breathing again and again the carbon dioxid 
that has come off from your own lungs, and do not be afraid 
to admit the night air to your room, for the same atmos¬ 
phere that surrounds houses during the day. surrounds them 
at night. 

Outdoor Sleeping. Every year more and more people are 
sleeping outdoors. It was long ago noticed that people who 
lived much in the open air were not troubled with consumption 
as were those who lived indoors. Then it was found that 
sleeping outdoors often helped to cure consumption. People 
began to wonder why anything that helped to cure sick¬ 
ness might not also help to keep them from getting sick, 
so more and more of them are building upper porches 
and other places where they can conveniently sleep in the 
open air. 

It is probable that the benefits of outdoor sleeping come 
from spending the long time when one is in bed in an 
atmosphere that is as free as possible from carbon dioxid. 
With this amount of time spent in the pure outdoor air, 
the body becomes so well and strong that it can kill off 
the disease germs that get into it. A well-ventilated house 
helps to preserve the health; walking and other exercises 
that require spending time in the open air are also healthful; 
but outdoor sleepers think their way of obtaining fresh air is 
the best of all, because in this way most of them spend more 
time in the outdoor air than they could possibly do in any 
other way. 

Summary. The lack of fresh air is the greatest evil that 
accompanies indoor life. Oxygen and carbon dioxid are the 
important gases of the air from the standpoint of the health 


VENTILATION 


185 


Ten per cent of oxygen is enough for the body, so we rarely 
suffer because there is not enough oxygen in the air. The 
carbon dioxid is poisonous to the human body, and to get 
rid of it is the problem of ventilation. Each person should 
have 600 cubic feet of room space and 3000 cubic feet of 
fresh air per hour. It is especially important that the sleep¬ 
ing room be well ventilated, because much time is passed in 
the atmosphere of this room. Outdoor sleeping is a healthful 
practice which is probably beneficial because it furnishes the 
sleeper with plenty of fresh air. 

QUESTIONS 

Of what two gases is the air chiefly composed ? Name one other 
gas that is found in small quantities in the air. What per cent of 
the air is oxygen? What per cent of expired air is oxygen ? What 
per cent of carbon dioxid is in ordinary air ? in expired air? What 
is the effect of breathing a small amount of carbon dioxid? of long- 
continued breathing of carbon dioxid? of breathing large quantities 
of carbon dioxid? What do miners call carbon dioxid? 

How much fresh air is needed by a man when he is at rest ? by 
a working man? by a boy? In public buildings, how much space 
should there be for each person? in sleeping rooms? Why is more 
air needed where lamps or gas jets are burning? How can one tell 
when the air in a room is bad? 

In ventilating, why should the opening by which the air passes out 
be near the floor? What is necessary for the satisfactory ventilation 
of crowded public buildings ? What systems of heating ventilate a 
room? What systems give no ventilation? Explain how a fireplace 
or stove brings fresh air into a room. Give some ways of avoiding 
drafts in ventilation. What should be done while schoolrooms and 
churches are empty? Why should sleeping rooms be especially well 
ventilated? Is night air unhealthful? From what do the benefits of 
outdoor sleeping probably come ? 


CHAPTER XIV 


THE KIDNEYS AND THE BODY WASTES 

Sometimes the body is well; sometimes it becomes ill. 
Why is it strong and abounding in health at one time and at 
another time weak and ill? Usually not because it lacks 
food or oxygen, or because it is too hot or too cold, but be¬ 
cause there are poisons in the body that injure the cells. 

Sometimes the poisons that cause 
sickness are produced by disease 
germs (page 285). Frequently they 
come from our own cells. Our 
bodies constantly produce carbon 
dioxid and poisonous proteid wastes 
(urea and uric acid), 1 and without 
organs for throwing off these sub¬ 
stances, life for us would not be 
possible for even an hour. We 
have already learned how the car¬ 
bon dioxid is excreted from the 
body. In this chapter we shall 
study the kidneys, — the organs that 
remove the uric acid and urea from 
the blood. 

The Kidneys. The kidneys are 
two bean-shaped organs. They are 
fastened to the back wall of the 

1 There are other proteid wastes besides the urea and uric acid, but for the 
sake of convenience the others will be disregarded here. 

186 


RENAL VEIN RENAL ARTERY 



Fig. 90. The kidneys and 
the bladder as seen from behind. 







THE KIDNEYS AND THE BODY WASTES 187 

abdominal cavity, one on either side of the spinal column. 
Stored around the kidneys are great quantities of fat The 
function of the kidneys is to excrete urea , uric acid , and water. 
As the lungs purify the blood by removing from it carbon 
dioxid, so the kidneys purify the blood by taking out of it 
urea and uric acid. 



Fig. 91. A is a longitudinal section of a kidney, showing how the kidney tubules 
empty into the branches of the ureter. B is a kidney tubule enlarged to show the cor¬ 
puscle at its upper end, and the long, winding course the tubule follows before it 
empties into the ureter. C is a small portion of a tubule, showing how the walls of the 
tubule are built of cells. 

The Tubules of the Kidneys. The kidneys are composed 
chiefly of an enormous number of very fine winding tubes 
( tubules ). The tubules rise in little sacs (Fig. 91 B) and flow 

































188 


HUMAN PHYSIOLOGY 


together, forming larger tubules. These larger tubules all 
run to the inner side of the kidney, where they empty into 
the branches of the ureter (Fig. 91 A). 

The Renal Corpuscles. The corpuscle on the end of a 
kidney tubule consists of a double-walled sac and a tuft of 
blood vessels. The structure of a corpuscle is most easily 
learned by studying its development. 

When the kidney is being formed in a very young animal, 
the kidney cells arrange themselves so as to form tubes 



Fig. 92. The development of a renal corpuscle. The corpuscle is formed by a 
blood vessel pushing in the end of a kidney tubule. (After Bailey.) 

(Fig. 91 C). A small blood vessel grows up close against the 
end of a tube (Fig. 92 A) and begins to push it in (Fig. 92 B). 
The end of the tube then broadens out and forms a small round 
sac, which grows up around the blood vessel (Fig. 92 C). 
Meanwhile, the blood vessel twists about and divides up into 
capillaries, and continues pushing in the wall of the sac 
(Fig. 92 D and E), until at last the corpuscle consists of a 
bunch of little blood vessels buried in a narrow-mouthed 
pocket in the end of the sac. This pocket almost fills the 
sac (Fig. 91 B). 










THE KIDNEYS AND THE BODY WASTES 189 


How the Wastes are excreted from the Kidneys. When 
the blood is flowing through the capillaries in a renal cor¬ 
puscle, the wastes escape through the capillary walls. They 
then pass on through the inner walls of the sac into the tubule, 
and flow down the tubule to the ureter. Also, blood capilla¬ 
ries are abundant all through the kidneys, and along the 
course of the tubules, wastes from the blood pass into the 
tubules through the tubule walls. Drop by drop the millions 
of kidney tubules separate the wastes from the blood and 
empty them into the ureters, which carry the wastes to the 
bladder. 

Alcohol and the Kidneys. More commonly, probably, than 
any other organs of the body, the kidneys become diseased 
from alcohol drinking. The cells in the corpuscles and 
tubules of the kidneys should allow the wastes to pass 
through them, and at the same time they should hold back 
the food that is dissolved in the blood. Alcohol may cause 
the kidney cells to become diseased and to allow the foods to 
escape with the wastes. Sometimes the cells suffer from 
fatty degeneration, and still more commonly the connective 
tissue in the kidney increases greatly (page 102) and stran¬ 
gles the cells of the tubules. In Bright’s disease, which is 
much more common among alcohol drinkers than among 
abstainers, whole tubules die and the proteid foods are 
allowed to escape with the wastes. 

Summary. Ill health is often the result of poisoning of 
the cells. The kidneys are organs for removing the 
poisonous proteid wastes and water from the body. A 
kidney is composed of many fine tubules, each of which ends 
in a renal corpuscle. A tuft of blood capillaries is buried in 
each of the corpuscles and the wastes pass out from the 
blood into the tubules and down to the ureters. Alcohol 


HUMAN PHYSIOLOGY 


190 

causes kidney trouble, Bright’s disease being very common 
among drinkers. 


QUESTIONS 

To what is ill health frequently due? Where do these poisons 
come from? Locate the kidneys. What is deposited around them? 
What is their function? 

Of what is a kidney chiefly composed? Describe the course of 
the tubule. In what does a tubule rise ? Describe the development 
and structure of a renal corpuscle. How do the wastes get from the 
blood into the tubules? 

What should the cells of the kidney tubules do with the wastes and 
with the foods? What two diseased conditions of the kidneys does 
alcohol cause? What disease of the kidneys is common among 
drinkers ? 


CHAPTER XV 

THE SKIN AND THE BODY HEAT 


The Functions of the 
Skin. The skin has four 
functions. It forms a 
protective covering for the 
body , which keeps the 
more delicate tissues from 
being injured, and pre¬ 
vents disease germs from 
getting in among them. 

It is an organ of feeling , 
for most of the nerves of 
touch end in the skin. It 
regulates the heat of the 
body , permitting the body 
to cool off when it be¬ 
comes too warm, and 
keeping in the heat when 
the body becomes cold. 

Its other function is to 
assist the lungs and kid¬ 
neys in excreting water x from the body. 
layers, the epidermis and the dermis. 



SU3CUTANE0US 

UiER 


Fig. 93. A section of the skin. B is a small 
portion of a sweat gland, and C is a cross-section 
of a sweat gland enlarged to show that these 
glands are hollow tubes with walls composed of 
cells. 


The skin has two 


1 The lungs, kidneys, and skin give off so much water that we are compelled 
. to drink liquids to give the body a sufficient supply of water. You should under¬ 
stand, therefore, that when the skin excretes water, the object is to cool the body 
and not to get rid of the water. 

191 









192 


HUMAN PHYSIOLOGY 



Fig. 94. A section of the 
epidermis. The epidermis 
grows by the division of the 


Thickening of the Epidermis. The 

epidermis is the protective layer of the 
skin, and wherever unusual pressure 
comes on the skin, as on the soles of 
the feet or on the palms, the epider¬ 
mal cells multiply very rapidly and 
cause a great thickening of the outer 
layer of the epidermis. When con¬ 
stant pressure falls on a small area 
of epidermis, as sometimes happens 
when a tight shoe is worn, a corn, or 
little mound of epidermal cells, is built 
up. This can be relieved only by re¬ 
moving the pressure that caused the 
growth. It is much easier to prevent 
sorns than it is to cure them, and only 
properly fitting shoes should be worn . 1 
A wart is a place where the epidermal 
cells grow and multiply more than is 
natural, but the cause of warts is not 
known. In cancer, either the epider¬ 
mal cells or the connective tissue cells 


lower cells. Its outer cells dry . , . . . ,, 

and scale off. a papilla con- increase enormously and feed on the 

taining a touch corpuscle is Other body tissues. 

shown. The skin pigment is in The Color Q f the Skin Xhe color 

the lower cells of the epidermis. 

of the skin is due to pigment in the 
cells of the lower layers of the epidermis. The outer epider¬ 
mal layers are partially transparent, and we look through 
these and see the coloring matter in the lower cells. Expos- 


1 It is estimated that 58 per cent of Americans have corns, ingrowing nails, the 
bones of the feet bent out of shape, or other foot troubles. The question of 
properly fitting shoes is, therefore, one of considerable importance. 


THE SKIN AND THE BODY HEAT 


193 


lire to the sun or wind causes the coloring matter to become 
more abundant in the skin, and the skin, as we say, becomes 
tanned. A freckle is a spot in the epidermis where the pig¬ 
ment is especially abundant. It is probable that the use of 
the skin pigment is to protect the nerves and other delicate 
structures beneath the epidermis from the light of the sun. 

The Dermis and the Subcutaneous Layer. The second 
layer of the skin is the dermis. It is composed of connec¬ 
tive tissue in which there are blood vessels, lymphatic vessels, 
and nerves. The upper surface of the dermis is thrown into 
papillce that stand up like little mountain peaks under the 
epidermis. Some of the papillae contain blood vessels, and 
some of them contain touch corpuscles. In the lower part 
of the dermis considerable fat is stored. The subcutaneous 
layer lies under the dermis. It is a 
layer of loose connective tissue in 
which large quantities of fat are found. 

Sweat Glands. With a magnifying 
glass small pores can be seen in the 
skin, in some portions of the body as 
many as twenty-five hundred to the 
square inch. They are the mouths of 
sweat glands , which are little tubes 
composed of epidermal cells (Fig. 93). 

A sweat gland runs down through the 
epidermis and ends in a coil in the 
lower part of the dermis, or in the 
subcutaneous layer. 

The Function of the Sweat Glands. 

The function of the sweat glands is to 
cool the body by pouring out perspiration on the skin. Around 
the lower part of a sweat gland are many fine blood capillaries 



MOUTHS OF SWEAT GLANDS 

Fig. 95. The surface of 
the skin of the finger-tip, mag¬ 
nified to show the mouths of 
the sweat glands. In some 
parts of the skin the papillae 
are arranged in rows, giving 
the surface of the skin a 
ridged appearance. 









194 


HUMAN PHYSIOLOGY 


from which an abundant supply of lymph escapes. The water 
of the lymph passes on through the walls of the sweat gland 
into the opening in the center of the gland, and flows out on 
the skin. A little perspiration passes out through the sweat 
glands at all times, but usually the amount is so small that it 
passes off into the air as vapor without being noticed. On a 
hot day, however, or when the body becomes hot from 
exercise, the sweat glands work so rapidly that the water 
accumulates on the skin. 

How the Body is cooled by the Perspiration. The body is 
cooled by the evaporation of the perspiration on the skin. 
Pour alcohol or ether on your hand and allow it to evaporate 
and your hand will feel cold. This shows that a liquid in 
evaporating takes up heat. You can have the same fact 
proved to you by visiting an ice factory and seeing water 
frozen by the evaporation of ammonia, or by performing the 
following experiment: 

Note the height at which the mercury stands in a thermometer. 
Then cover the bulb of the thermometer with cotton, and wet the 
cotton with ether, chloroform, benzine, gasoline, or alcohol. Swing 
the thermometer through the air and then note the height of the 
mercury. What causes it to fall ? 

The Sweat Glands controlled by the Nervous System. The 

sweat glands are controlled by the nervous system, which 
causes them to work rapidly or slowly according to the heat 
of the body. That the sweat glands are connected with the 
nervous system is shown by the way embarrassment or pain 
may bring out the perspiration. 

The Hair. A hair grows in a small, deep pocket in the 
skin, called the hair follicle. At the bottom of the follicle is 
the hair papilla. This is a little mound of connective tissue, 
belonging to the upper layer of the dermis. The follicle is 


THE SKIN AND THE BODY HEAT 


195 


lined with and the hair papilla is covered over by cells which 
have been folded in from the 
epidermis. The hair rests 
on the papilla, and grows by 
the epidermal cells at the 
base of the hair multiplying 
and pushing the cells above 
them upward. A hair, like 
the epidermis, contains nei¬ 
ther nerves nor blood vessels. 

In the connective tissue of 
the papilla, however, is a rich 
blood supply, which brings 
food to the growing cells at 
the base of the hair. 

The Sebaceous Glands and 
the Muscles of the Hair. 

Opening off from the sides 
of the hair follicles are the 
sebaceous glands, which man¬ 
ufacture a clear, odorless oil 
for the hair. Small muscles 1 
are attached to the hair folli¬ 
cle in such a way that when 
they contract, the hair is made to stand on end. Doubtless 
you have seen the hairs on a cat’s tail or on a dog’s neck stand 
on end, and you probably know that in man great fright may 
cause these muscles to contract and make the hair stand up. 



Fig. 96. 


BLOOD VESSEL 

A hair in its follicle. 


1 The upper ends of these muscles are attached in the connective tissue just 
below the epidermis. Under certain conditions they contract and draw the epi¬ 
dermis down in little depressions, producing the condition that is called “goose 
flesh.” 








196 


HUMAN PHYSIOLOGY 


Care of the Hair. Brushing the hair is very beneficial to it 
because it spreads the oil from the sebaceous glands all along 
the hair. Brushing the hair also causes a good circulation of 
blood in the scalp, thus providing the growing cells of the 
hair with an abundance of food and oxygen, and promptly 
carrying away their wastes. The hair and. scalp should be 
washed occasionally with good soap to remove dust and oil. 
A little ammonia or borax in the water is useful when the 
hair is very oily, but if this treatment causes the hair to 
become dry and brittle, only soap and water should be used. 

Dandruff and Baldness. It is thought that dandruff is 
caused by a germ that grows in the sebaceous glands and 
the scalp, and that this disease maybe spread by hair brushes 
and combs. It is, therefore, safest not to use the combs and 
brushes that are found in public places. 

Baldness is supposed usually to be caused either by dan¬ 
druff or by tight hats that cut off the blood from the scalp. 
Notice persons who are bald and you will find that usually 
the bald part of the head is the part that is covered by the 
hat. When a hair falls out, a new hair will take its place, pro¬ 
vided the epidermal cells that line the lower part of the hair 
follicle and cover the hair papilla are not destroyed. If these 
are destroyed, the hair will not be renewed. 

The Nails. A nail is formed from the upper horny layer 
of the epidermis. Its growth is chiefly at the base, as you 
will know if you have seen a spot 1 grow forward on a nail 
until it reached the tip. The nail cells turn to a horny sub¬ 
stance, and the nails have a pink appearance because the rich 
blood supply below can be seen through them. Where the 
cells are young, the blood cannot be seen so plainly through 

1 A black spot on a nail is caused by injuring the blood vessels under the nail, 
thus allowing the blood to flow out and form a clot. 


THE SKIN AND THE BODY HEAT 


197 

them, and there is, therefore, a white area at the base of each 
nail. 

When a nail is injured, or lost through accident, it will 
grow again, provided the bed of epidermal cells on which the 
nail rests and from which it grows is not destroyed. But if 
the “ roots of the nail ” are destroyed, the nail will not be re¬ 
placed. The nails protect the fingers, and assist in picking 
up small objects. 


THE BODY HEAT 

A man in the cold Arctics loses much more heat than does 
a man living in the warm tropics. Yet the temperature of the 
human body all over the world is the same. A man who is 
violently exercising produces five or six times as much heat 
as a resting man produces. Yet the temperature of the 
human body in exercise and rest is nearly the same. In 
health, the human body keeps a temperature of about 98J 
degrees, varying only about one . half of a degree above or 
below this point. 

The Regulation of the Body Heat. On a cold day we can 
close the doors and windows of a room and with a small fire 
keep the temperature of the room at 70 degrees, or we can 
open a window and still keep the temperature of the room at 
70 degrees by firing up and producing more heat. We can 
control the temperature of the room either through the 
amount of heat that is lost, or through the amount of heat 
that is produced. So the temperature of the human body can 
be kept at 98degrees either by regulating the amount of 
heat that escapes from the body , or by regulating the amount 
of heat produced in the body. Both of these methods are 
used in our bodies. 


198 


HUMAN PHYSIOLOGY 


Regulating the Escape of Heat The skin governs the 
escape of heat from the body in two ways. The first way 
is by regulating the amount of blood that comes out into the 
skin. When the body is cold, the blood vessels of the skin 
contract and keep the blood in the warm internal parts of 
the body. When the body is hot, the vessels,in the skin open 
up and allow a larger amount of blood to come to the outside 
of the body where it will be cooled. 

The other method of regulating the escape of the heat is 
through the sweat glands. When the heat of the body rises, 
the sweat glands cool the body by pouring out perspiration 
on the skin. Both the vessels of the skin (page 145) and the 
sweat glands are governed by the nervous system, so it is the 
nervous system that regulates the amount of heat that escapes 
from the body. 

Regulating the Amount of Heat produced. When the body 
is exposed to severe cold, much heat escapes from it, and the 
cells burn an extra supply of food to keep the body tempera¬ 
ture up to 98^ degrees. For this reason, men living outdoors 
in cold weather require great quantities of food (page 124). 
For the same reason, an animal that is kept outdoors in the 
winter needs more food than the same animal requires when 
it is kept in a warm stable. 

The Temperature of the Body in Illness. When one is weak 
and ill, the body temperature sometimes falls below normal, 
not enough heat being produced or too much heat being lost. 
Sometimes the sweat glands work when they should not do 
so, as in the night sweats which accompany consumption and 
other weakening diseases. More commonly the temperature 
rises above 98^ degrees, when one is said to have fever. 

The Cause of Fever. In fever there is usually a greater 
breaking down of the tissues and a greater production of 


THE SKIN AND THE BODY HEAT 


199 


heat than is natural. Not nearly so much heat is produced 
in fever, however, as in violent exercise, and the main cause 
of a fever is that not enough heat is lost. Usually the trouble 
is that the sweat glands refuse to work. The crisis or turn 
of a fever is usually marked by the sweat glands beginning 
their work, the surplus heat escaping and the feVer going 
down from that time. 1 

Chills. In illness the skin usually is hot and flushed with 
blood, but sometimes the blood vessels of the skin are tightly 
closed and the blood is kept from coming to the outside of 
the body where it will be cooled. Then the skin has no 
warm blood, and the person has a chill and feels cold, even 
when the inner parts of the body are in a hot fever. 

The Extremes of Body Temperature. The human body is 
very sensitive indeed to changes in temperature, and will die 
if its heat falls far below or rises much above normal. One 
hundred and two degrees is warm fever, and 104 degrees is 
a hot fever; 105 degrees, if it continues for long, is danger¬ 
ous, and when a fever rises to 109 or 110 degrees, it is almost 
surely fatal. How far below normal the temperature can 
fall without fatal results depends on how long-continued the 
decline is, but 91 or 92 degrees will cause death in a very 
short time. 

1 Sometimes, in slight fevers, a hot bath, followed by an extra heavy covering 
of the body for a time, will start the sweat glands and lower the fever. Rubbing 
with alcohol quickly cools the body, because the alcohol evaporates very rapidly. 
Sponging with water cools the skin in the same way, but not so rapidly. Some¬ 
times, in long-continued illness, where the temperature goes so high that there is 
danger of death from the fever, it is best to take the heat out of the body with 
ice packs or an ice-cold bath. But this (as well as rubbing with alcohol) is a 
shock to the nervous system, and it drives the blood inward and checks instead 
of starting the sweat glands. It should be used only when a physician advises it, 
or when the fever runs so high that it must be quickly lowered. Sponging with 
warm or tepid water is safer, and is often sufficient. 


200 


HUMAN' PHYSIOLOGY 


BATHING 

Dead epidermal cells of the skin and oil from the seba¬ 
ceous glands become mixed with perspiration and dust and 
form a considerable amount 1 of waste matter on the skin. 
This should be removed, or it will form a breeding place for 
many germs, which may get down into the hair follicles and 
cause pimples and other skin troubles. 2 It is important, 
therefore, to keep the skin clean, and to do this, soap should 
be used on the skin to dissolve the oily matter. For purposes 
of cleanliness, a moderately warm bath is best, but aside from 
cleansing the skin, bathing has little effect on the body except 
through the temperature of the water. A hot or cold bath, 
however, may have a decided effect on the nervous system, 
and through it, on the whole body. 

Cold Baths. When a cold bath is taken, the blood vessels 
of the skin contract and send the blood to the heart, lungs, 
brain, and other internal parts of the body. This quickens 
the circulation and respiration, and causes more food to be 
oxidized in the body, thus producing more body heat. After 
the bath, the reaction (the return of the blood to the skin) 
usually comes, warming and reddening the skin, and giving 
the bather a fresh and pleasurable feeling. Rubbing the 
skin helps to bring on the reaction. Sometimes when the 
water is very cold, or the person taking the bath is weak or 
unaccustomed to cold baths, the reaction does not follow, and 
the bather is left weak and shivering. This is decidedly 
injurious. A person should train himself gradually to a cold 
bath, and should always be sure that the temperature of the 
water is not so low, and the time spent in the bath not so 

1 It has been estimated that a pint of epidermal cells scale off one arm and 
hand in a month. 2 Blackheads are hair follicles that have become stopped up. 


THE SKHST AND THE BODY HEAT 


201 


long, that the reaction will not come promptly. Some indi¬ 
viduals do not seem able to accustom themselves to cold baths 
without too great a shock to the nervous system, and these 
persons should bathe only in warm or tepid water. 

Warm Baths. Most of the effects of a hot bath are exactly 
opposite to the effects of a cold bath. A hot bath opens the 
vessels in the skin, and draws the blood to the surface of the 
body and away from the muscles and the internal organs. 

Time for bathing. Since a cold bath sends the blood to 
the brain and causes a greater amount of food to be oxidized 
in the body, the best time to take such a bath is in the morn¬ 
ing, when we wish to have our energies aroused and to wake 
up for the work of the day. It should not be taken when one 
is very hot or tired. The bes't time for a warm bath is just 
before bedtime, after the work of the day is done. Persons 
who are troubled with insomnia (sleeplessness) sometimes 
find that a warm bath enables them to go to sleep. One who 
has been engaged in very hard exercise will find that a hot 
bath draws the blood away from the muscles to the skin. 
A warm bath should not be taken immediately before or 
after eating, because it draws the blood from the digestive 
organs. Tepid baths have no particular effect on the body, 
and may be taken at any time. Unless the water is cold, a 
swim, like other exercise, may be taken at almost any time 
except just before and for a time after eating. 1 

1 It is well to know that “ cramps,” with which swimmers are occasionally 
seized, is believed to come on more frequently after eating. Just what the trouble 
is in cramps is not well understood. One theory is that when the diaphragm is 
hindered in its downward movement by a full stomach, the severe exercise of 
swimming and the force required to push out the body walls in the water, throws 
so heavy a task on the respiratory muscles that these muscles suddenly fail in 
their work and the breathing stops. Whether or not this theory is correct, it is 
probably best to follow the old rule of not taking a swim for two hours after eating. 


202 


HUMAN- PHYSIOLOGY 


THE HEATING OF BUILDINGS 

The lower animals depend on the food which they burn in 
their bodies to keep up their heat, but man has learned the 
use of fire, and in the colder portions* of the earth heats his 
houses. This has many advantages, but it has certain dis¬ 
advantages ; for when we pass from a warm house into cold 
winter air, there is suddenly a very great change in the 
amount of heat that is lost from the body. 

Overheated Rooms. Many rooms both in private dwell¬ 
ings and in schoolhouses and other public buildings are kept 
too hot. This is injurious for the following-reason : 

In a warm room the skin is moistened with perspiration 
and the blood is drawn to the surface of the body. When a 
person passes from a warm room to the cold outside air, the 
perspiration on the skin continues to evaporate and take heat 
out of the body, and large amounts of heat are lost before 
the blood can be cut off from the skin. An overheated 
room is injurious because on leaving it too much heat is lost 
from the body , and the body is chilled. Sitting down to rest 
in the cold outside air when one is hot fipm exercising may 
in the same way cause the body to be chilled. 

Underheated Rooms. Cold rooms are injurious because in them 
the body loses too much heat and becomes cold and chilled. Cold 
floors are common, and little children, especially, suffer from 
them. The temperature of the air at the floor of a room is often 
20 degrees lower than the temperature of the air a few feet 
above the floor. When small children get down to play on the 
floor they may be passing from a warm to a cold atmosphere, and 
they often suffer from cold in a room that in some parts is suffi¬ 
ciently heated. Fires should be built on cold days in the spring 
and fall, or colds will follow staying in rooms that are too cool. 


THE SKIN AND THE BODY HEAT 


203 


How chilling the Body injures it. The most common 
result of chilling the body is a cold. It is practically certain 
that a cold is a germ disease, and it is thought that allow¬ 
ing the body to become too cold weakens it, so that the 
germs can grow in it and cause the cold. One great ad¬ 
vantage that is claimed for cold baths is that by training 
the vessels of the skin to close quickly they prevent the 
body from becoming chilled and give those who take them 
marked freedom from colds. 

The Use of the Thermometer. About 70 degrees is the 
proper temperature for a room in which people are sitting. 
In keeping a room at the proper temperature, a thermometer 
is a very great aid. The temperature of different parts of 
the room should be tested and some method of heating used 
that will warm all parts of the room as evenly as possible, so 
that some of the people in the room will not be too hot while 
others are too cold, or one part of the body be warm while 
another part of it is cold. Some persons prefer rooms heated 
to 75 or 80 degrees, and if a schoolroom is not provided with 
a thermometer, there is great danger that the whole roomful 
of children will be kept too warm. Where rooms are heated 
with stoves, it will be found that a large stove gives a more 
steady, even heat than a small stove gives. Having one part 
of the body hot and another part cold is decidedly injuribus, 
so cold floors and cold drafts are to be avoided wherever 
possible. 

CLOTHING 

Birds have feathers and most mammals have a coat of hair 
to retain the body heat, but in man the hair on the body is so 
fine and thin that it is of little use as a protection from the 
cold. In the colder regions of the earth, man has, therefore, 


204 


HUMAN PHYSIOLOGY 


been compelled to clothe himself to keep up his body heat. 
The chief physiological use of clothing is to retain the body heat. 
Clothing also saves the body from wounds and bruises and 
protects it from the heat and light of the sun. 

How Clothing retains the Body Heat. Heat passes with 
great difficulty through dry air, and clothing prevents the 
escape of the body heat chiefly through holding air in the 
little crevices in the cloth. The fur of animals forms a very 
warm body covering, and in a number of animals (including 
the cat, rabbit, and sheep) it has been found that on an average 
about 2 per cent of the fur is hair, and 98 per cent of it is 
air that is held in the little spaces between the hairs. 

The Best Materials for Clothing. Woolen clothing is 
warmer than cotton or linen. Wool is therefore the best 
material for winter clothing, but in hot summer weather, cot¬ 
ton and linen clothing may be superior to woolen. Woolen 
clothing is warmer than the others because it has many little 
air spaces between the threads; in cotton and linen cloth 
the threads are harder, and are woven more solidly together, 
so that a smaller amount of air is held in the cloth. 

Wool is superior to cotton and linen for winter clothing for 
another reason, also. It will absorb more water than either 
of the others, and therefore does not become dampened so 
quickly by the perspiration. Cold water or cold, wet clothing 
touching the skin takes the heat out of the body with great 
rapidity, and if a person clothed in cotton or linen exercises 
until he perspires, his clothing becomes damp; then if he 
rests in a cold atmosphere the heat may escape too rapidly 
from the body, and a cold follow. 

Tight-fitting and Insufficient Clothing. Tight clothing, by 
interfering with the circulation of the blood, may cause cold¬ 
ness in some parts of the body. Cold feet are often caused 


THE SKIN AND THE BODY HEAT 


205 


by tight shoes, or by tight clothing around the legs that pre¬ 
vents the descent of the warm blood to the feet. Insufficient 
clothing on the legs also causes cold feet, because cold on the 
legs causes the arteries in them to contract, and lessens the 
amount of blood that is supplied to the feet. Many children 
suffer from being dressed in stockings so short that they leave 
a portion of the leg uncovered. It is important not only that 
sufficient clothing be worn but that the clothing be so distrib¬ 
uted on the body, that all parts of the body will be kept warm. 

Other Hygienic Points connected with Clothing. Wet cloth¬ 
ing takes the heat out of the body and is especially likely to 
cause colds. Damp feet are a common cause of sickness, and 
when rubbers are needed to keep the feet dry they should 
always be worn. 

Wearing heavy clothing indoors has the same effect as 
staying in an overheated room. An overcoat should not 
be worn in the house, but should be put on before going out¬ 
doors, to protect the body from the sudden change to the cold 
of the outside air. 

Heavy clothing should be worn in the spring and fall when 
the weather demands it. If in the spring the weather turns 
cool after heavy clothing has been taken off, the heavy cloth¬ 
ing should be put on again. The clothing and the heating 
of buildings should be adapted to the weather., and if thin 
clothing is worn and fires are allowed to go out on cold 
days in the spring and fall, colds and sickness will follow. 

Summary. The skin forms a protective covering for the 
body, is an organ of feeling, regulates the body heat, and 
excretes water. The outer layer of the skin is called the 
epidermis. The dermis is a layer of connective tissue under 
the epidermis, and the subcutaneous layer lies below the 
dermis. Fat is stored in this layer. 


20 6 


HUMAN PHYSIOLOGY 


The sweat glands take water from the blood and pour it 
out on the skin as perspiration. By the evaporation of the 
perspiration the body is cooled. The sweat glands are under 
the control of the nervous system. 

A hair grows in a hair follicle and rests on a hair papilla. 
It grows from the epidermal cells at its base. The sebaceous 
glands secrete a clear oil for the hair. Brushing and a clean 
scalp are beneficial to the hair. Dandruff is in all probability 
a germ disease and may be contracted from brushes and 
combs that other persons have used. Baldness is usually due 
to dandruff or tight hats. 

The nails grow from the epidermis. They protect the 
fingers and are useful in picking up small objects. 

The temperature of the healthy human body is always near 
98J degrees. The skin regulates the escape of heat from the 
body by controlling the amount of blood that comes to the 
skin and by the action of the sweat glands. The amount 
of heat produced in the body is regulated by the amount of 
food that is oxidized, extra food being burned when the body 
is cold. 

In sickness the temperature of the body may rise too high 
or fall too low. The chief trouble in fever is that not enough 
heat is lost, the sweat glands usually failing to work. In a 
chill the blood is cut off from the skin. 

The skin should be kept clean so that germs will not find 
food on it. 

A cold bath is best taken in the morning and a warm bath 
at bedtime. Cold baths are injurious when they are not 
promptly followed by the reaction. 

Overheated rooms cause the body to be chilled after leav¬ 
ing them; underheated rooms cause the body to be chilled 
while in them; and chilling of the body is followed by colds. 


THE SKIN AND THE BODY HEAT 


207 


A thermometer should be used to determine whether rooms 
have the proper temperature. 

Clothing retains the heat by holding air in its pores. 
Wool is a warmer material for clothing than cotton or linen. 
Tight-fitting clothing causes coldness of parts of the body by 
interfering with the circulation. Wet clothing, wearing heavy 
clothing indoors, and insufficient clothing during cold weather 
in the spring and fall are causes of sickness. 


QUESTIONS 

Give the four functions of the skin. Name the layers of the skin. 
What is a corn? What gives the color to the skin? What is a 
freckle ? 

Of what is the dermis composed? What is a papilla? Where 
is the subcutaneous layer? Of what is it composed, and what is 
deposited in it? 

What are the pores in the skin? Describe a sweat gland. What 
is the function of the sweat glands? Where does the water of the 
perspiration come from ? Why do we not see the perspiration on 
the skin at all times? How does perspiration cool the skin? What 
controls the sweat glands? 

What is a hair follicle? a hair papilla? With what is the follicle 
lined and the papilla covered? When the hair grows, where do the 
cells multiply? From what layer of the skin is the hair formed ? How 
does a hair get food ? Where are the sebaceous glands ? What is 
their function ? What causes the hair to stand on end ? 

Give two reasons why brushing benefits the hair. What is the 
cause of dandruff? How may this disease be contracted? What 
causes baldness? 

From what layer of the skin are the nails formed? What causes 
their pink color? What causes the white spot at the base of a nail? 
What is the function of the nails? 


20 8 


HUMAN PHYSIOLOGY 


What is the temperature of the body in health ? Give two ways by 
which the body heat is regulated. In what two ways does the skin 
regulate the escape of the heat from the body? How do the cells 
regulate the amount of heat produced? Why must persons living 
outdoors have more heat than those who live indoors? 

What is fever? What is its cause? What causes a chill? 

Why should the skin be kept clean? Give the effect of a cold 
bath on the blood vessels of the skin. Give some other effects of 
a cold bath. When is a cold bath injurious? 

Give the effect of a warm bath on the vessels of the skin ; on the 
distribution of the blood. When should a cold bath be taken? a 
warm bath? Why is a warm bath harmful immediately before or 
after eating? What is the effect of a tepid bath? Why should one 
not take a swim immediately after eating? 

Why are overheated rooms injurious? underheated rooms? How 
does chilling the body injure it? How do cold baths prevent this? 
What is the proper temperature for a living room ? Why is the use 
of the thermometer important? 

What is the chief physiological use of clothing ? How does clothing 
retain the body heat? Which is the warmest material for clothing? 
Why? Which material absorbs moisture best? What is the effect of 
tight clothing on the heat of the body? Why should the feet be kept 
dry? What is the effect of wearing heavy clothing indoors? At what 
time of the year should especial care be taken to wear sufficient 
clothing? 


THE SKIN AND THE BODY HEAT 


209 


REVIEW QUESTIONS 

Chapter XI. Why is the circulation of the blood necessary? 
Trace the blood from right auricle to right auricle. What does the 
blood lose and gain in the capillaries of the body ? of the lungs ? 
How is the oxygen carried in the blood? What is lymph? How is 
it returned to the blood? What is the function of a lymph node? 
Mention some common causes of injury to the heart. 

Define : auricle ; ventricle ; artery; vein ; capillary ; hemoglobin ; 
plasma; thoracic duct. 

Chapter XII. What is the object of respiration? Why is oxygen 
necessary to the body? Why must the body get rid of its carbon 
dioxid? What does the air gain and lose in the lungs? Why does 
mouth breathing cause disease? Name five points connected with 
the hygiene of the respiratory organs. What kind of diseases chiefly 
affect these organs? How is voice produced? How are the vocal 
cords thrown into and out of action ? 

Define : pleura; diaphragm ; uvula; larynx ; epiglottis ; bronchial 
tubes ; mucus ; cilia; thyroid ; cricoid ; arytenoid. 

Chapter XIII. Why is ventilation necessary? How much fresh 
air does a person need in an hour? How much air space for each 
person should there be in a public building? in a private house? 
Explain how a fireplace or stove ventilates a room. Why is the ven¬ 
tilation of sleeping rooms especially important? 

Chapter XIV. What is the usual cause of illness? How are the 
poisons that are in the body produced? What is the function of the 
kidneys? Explain how the wastes get from the blood into the 
ureters. What diseases of the kidneys are caused by alcohol? 

Define : uric acid ; renal corpuscle. 

Chapter XV. Give four functions of the skin. Explain how the 
perspiration gets from the blood to the surface of the skin. Draw a 
diagram of a hair in its follicle. What is the temperature of the 
human body? How is the escape of the heat from the body con¬ 
trolled? When is a cold bath injurious? What is the danger from 
an overheated room? from a cold room? Mention some hygienic 
points connected with clothing. 

Define : epidermis ; dermis; papilla; follicle ; sebaceous. 


CHAPTER XVI 


THE NERVOUS SYSTEM 

The first great work of the nervous system is to cause all 
the parts of the body to work harmoniously together. The 
second is to act as the organ of the mind} In a former chap¬ 
ter we learned something of the way the body is ruled, and 
we have seen in a general way how the different organs are 
controlled and kept at work. In this chapter we shall take 
up in more detail the structure and the function of the ner¬ 
vous system. 

Nerve Cells and Nerve Fibers. Nerve tissue contains nerve 
cells and nerve fibers. The nerve cells are much branched, 
are larger than most of the body cells, and have a gray color. 
Most of them are found in the brain 2 and spinal cord, but 
small groups of nerve cells called ganglia 3 (singular, gang¬ 
lion) are found in various parts of the body. 

1 A simple and easy way of treating of the relation between the brain and the 
mind is to say that the mind is in the brain, and that it is the cells of the brain 
that think and feel. It may be objected, however, that we do not know where 
the mind is ; that it can exist apart from the body altogether ; and that while the 
function of the muscle cells is to contract, and the function of gland cells is to 
secrete, it is perhaps not allowable to say that the function of the brain cells is to 
think. The brain, however, is in some way closely associated with the mind, and 
we have therefore spoken of it as the organ of the mind. 

2 It is estimated that there are 1,200,000,000 cells in the gray matter on the 
surface of the cerebrum. 

3 There is a ganglion on the root of each spinal nerve (Fig. 103), but most of 
the ganglia belong to the sympathetic system (Fig. 106). They are found chiefly 


210 


THE NERVOUS SYSTEM 


211 


A nerve fiber contains a gray central axis cylinder , which 
is a branch of the cytoplasm of a 
nerve cell. A nerve fiber is there¬ 
fore always connected with a nerve 
cell and may almost be considered 
as a branch of a cell. A nerve cell 
and nerve fiber taken together are 
called a neuron. The nerve mes¬ 
sages, which are also called stimuli 
and nerve impulses , travel through 
a fiber in the gray central axis 
cylinder. 

Efferent and Afferent Nerve 
Fibers . 1 The nerve fibers in which 
the impulses travel prom the brain 
and cord are called efferent fibers. 

They take messages to the muscles 
which cause the muscles to contract, 
and to all the glands and organs 
of the body, causing each to work. 

The fibers which carry impulses 
from the different parts of the 
body to the brain and cord are 
called afferent fibers. 

The Nervous System as a Con¬ 
nector of the Body Parts. As you 


in the internal parts of the body, and are not 
found in the limbs, or to any extent among the 
voluntary muscles. Many of them are micro¬ 
scopic. 

1 Efferent and afferent nerve fibers are often 
called motor and sensory fibers. 








212 


HUMAN PHYSIOLOGY 


will understand better after studying reflex actions, a great 
portion of the work of the nervous system in governing the 
body is done by putting the different body parts into com¬ 
munication with each other. In a former chapter (page 23) 
we have spoken of the nervous system as the ruler of the 
body. In reality, it resembles a telephone system as much 



FlG. 98. A shows the number of wires necessary to connect twelve houses by tele¬ 
phone without a central office. B shows the number of wires necessary to connect the 
same number of houses through a central office. The number of nerve fibers that 
would be necessary to connect all parts of the body without a brain and spinal cord 
to act as a central office can hardly be imagined. 

as it does a monarch. As on a telephone system the dif¬ 
ferent houses are put into connection with each other 
through a central office, so the different parts of the body 
are connected through the brain and spinal cord. In many 
parts of the body each cell is supplied with a nerve fiber 
(Fig. 102) and the body has in it a perplexing network of 
nerves. By examining Figure 98, you can understand what 
a hopeless tangle the nervous system would become if an 
attempt were made to connect all the cells of the body with¬ 
out a brain and spinal cord to act as a central office. 
















THE NERVOUS SYSTEM 


213 


THE CENTRAL NERVOUS SYSTEM 

The central nervous system consists of the brain, the spinal 
cord, and the nerves arising from the brain and cord. Twelve 
pairs of nerves pass out from the brain, and thirty-one pairs 
from the cord, putting these nerve centers in connection with 
all the body parts. 

The Brain. The spinal cord is only a little thicker than a 
lead pencil. The brain fills the whole cranial cavity. The 



FIG. 99. Longitudinal section of the brain. 


spinal cord of a man weighs about an ounce. The brain 
weighs about fifty ounces. The brain, therefore, composes 
by far the greatest part of the central nervous system. Its 
three main divisions are the cerebrum, the cerebellum, and 
the medulla oblongata. 

The Cerebrum. The cerebrum comprises more than three 
fourths of the entire brain. It is divided by a deep groove in 


214 


HUMAN PHYSIOLOGY 


its upper surface into a right and a left hemisphere. The sur¬ 
face of the cerebrum is thrown into a great number of folds 
and wrinkles called convolutions (Fig. 13). 

A layer on the surface of the cerebrum is composed of 
nerve cells, and therefore has a gray color. This is the gray 
matter of the brain, with which the mind is associated. The 
inner and lower parts of the cerebrum are chiefly composed 
of nerve fibers. 

The Fibers of the Cerebrum. A great network of fibers 
connects all the different parts of the cerebrum with 
each other. Other fibers connect 
the cerebrum and the cerebellum, 
and countless fibers run through the 
medulla into the spinal cord, and 
connect the cerebrum with the body 
parts below. In the medulla most 
of the fibers from the cerebrum cross 
so that the right hemisphere of the 
cerebrum is connected with the left 
side of the body, and the left hemi¬ 
sphere is connected with the right 
side of the body. If, because of 
injury or of apoplexy, a blood clot 
forms on the right side of the cere¬ 
brum, it will bfc the left side of the body that will be 
paralyzed. 

Functions of the Cerebrum. The cerebrum has three func¬ 
tions : 

The cerebrum is the seat of the mind. When the cerebrum 
of a pigeon or of a dog is removed, life may go on, but all 
memory and reason are lost, and the animal is hopelessly 
idiotic. Removing the gray matter on the surface of the 



Fig. ioo. The cerebrum 
from above, showing the hemi¬ 
spheres. 


THE NERVOUS SYSTEM 


215 


cerebrum has the same effect on the intelligence as re¬ 
moving the whole cerebrum. 

The cerebrum is the seat of the sensations. Nerve messages 
from all parts of the body come into the cerebrum and 
cause the sensations of light, sound, taste, smell, touch, heat, 
cold, hunger, fatigue, and other sensations. Without a 
cerebrum an animal has no mind, and without a mind there 
could, of course, be no knowledge of the afferent nerve 
impulses and no such thing as a sensation of pain, cold, 
hunger, or any other kind of sensation. 

The cerebrum originates and sends out impulses that cause 
voluntary movements. When we decide to move, the cere¬ 
brum can start out impulses which cause the muscles to con¬ 
tract. We have, therefore, the power of voluntary movement 
—the power to make the muscles work when we wish them 
to do so. 

The Cerebellum. The cerebellum lies behind and above 
the medulla, and is covered over by the back lobes of the 
cerebrum. Many nerve fibers connect the two sides of the 
cerebellum with each other. The cerebellum is also con¬ 
nected with the cerebrum, and through the medulla and cord 
with most of the body. The cells in the cerebellum are 
mainly in a layer on the surface, and the fibers in its central 
lobe are arranged so that they form a tree-like mass of white 
matter, called the arbor vitcz (“tree of life ”). 

Function of the Cerebellum. There is much dispute about the 
function of the cerebellum, but it seems to be about as follows : 

The cerebellum causes all the muscles to keep a proper 
amount of contraction. When the cerebellum is injured, all 
the muscles are relaxed, instead of keeping a certain amount 
of contraction as they usually do. The result is trouble in 
the movements, because when the cerebrum causes a muscle 


216 


HUMAN PHYSIOLOGY 


to contract, the antagonistic muscle does not work in opposi¬ 
tion and steady the motion. This causes jerky movements 
and movements that often go too far (page 67). 

The second function of the cerebellum is to assist in coor¬ 
dinating the movements of the muscles of locomotion. When 
a man’s cerebellum is injured, he staggers about as though 
he were intoxicated. His muscles are not paralyzed, but 
some of them contract too powerfully, some not powerfully 
enough, and often they fail to contract at the right moment. 
The cerebellum seems to cause the muscles that are used in 
standing, walking, and running to act in an orderly manner, 
and thus keeps the body from falling. 

The Pons. The pons lies in the pathway between the dif¬ 
ferent parts of the brain, and it is composed chiefly of fibers 
that connect the cerebrum, cerebellum, and medulla. There 
are also in the pons many fibers that connect the two sides of 
the cerebellum. From one side of the cerebellum the fibers 
pass forward to the pons, cross over in it, and turn backward 
into the other side of the cerebellum. The word “ pons ” 
means a bridge, and the pons is a bridge connecting all parts 
of the brain. 

The Medulla. The medulla contains many nerve fibers 
that connect the higher parts of the brain with the spinal 
cord and the body. The greater part of the head and many 
of the internal organs, including the heart and lungs, are sup¬ 
plied by nerves that rise from the medulla. When the cere¬ 
brum is removed from an animal, the intelligence is lost, but 
life may go on; when the cerebellum is injured, the control 
of the muscles is lost; but when the medulla is injured, death 
comes at once because the breathing stops. 

The Function of the Medulla. The medulla conducts stimuli 
to and from the higher parts of the brain , and it acts as a reflex 


THE NERVOUS SYSTEM 


217 


center for the parts of the body that receive nerves from it. 
To understand what is meant by a reflex center we must 
know what a reflex action is. Before taking up this subject 
we shall discuss the spinal cord, for like the medulla the 
spinal cord is a reflex center. 

The Spinal Cord. The inner part of the spinal cord is 
composed of gray matter (cells) and the outer part of white 
matter (fibers). All the skin and the voluntary muscles of 
the body parts below the neck are supplied by the thirty-one 
pairs of spinal nerves, and through the sympathetic system 
the spinal cord is connected with the internal organs, the 
sweat glands, and the blood vessels. 

Functions of the Spinal Cord. The spinal cord has the same 
two functions as the medulla. The first of these functions is 
to conduct impulses to and from the brain. The nerve impulses 
that come in through the spinal nerves pass up to the brain 
through the cord, and the nerve impulses sent out by the 
brain to the glands and muscles come down through the 
cord. For this reason, if the spinal cord be cut across, all 
parts of the body supplied by nerves from below the cut 
lose their feeling and are paralyzed. The impulses from 
these parts cannot get up to the brain to cause sensations 
of feeling, and the commands of the brain cannot get to the 
muscles below the cut to cause them to move. The other 
function of the spinal cord is to act as a reflex center. 

Reflex Actions. Reflex actions are actions that are caused 
by impulses which start in afferent nerves. An example 
will give the clearest idea of a reflex. 

Suppose you burn your finger by touching a candle flame 
(Fig. ioi). The heat starts an impulse up the afferent nerve 
fibers. The impulse passes into the spinal cord, then into 
the efferent nerve, and traveling down to the muscles of the 


218 


HUMAN PHYSIOLOGY 


arm, causes them to contract and jerk the hand away. An 
impulse also goes on up to the brain and causes a sensation 
of pain, but the hand is moved before the pain is felt. 

An action like this is a reflex action. It differs from the 
action when you voluntarily move your hand in the place in 
which the nerve impulse starts. In the voluntary action, the 
brain originates and starts out the impulse. In the reflex 



Fig. ioi. Diagram illustrating reflex action. The impulse starts in the finger and 
passes through the spinal cord to the muscle of the arm. D shows the way the con¬ 
nections between the neurons are made in the cord. 


action, the impulse starts in the outer ends of the nerves, goes 
into the cord, and comes back down the nerves to the muscles. 
In this action the spinal cord makes the connection betzveen the 
afferent and efferent.neurons. 

Could a reflex be carried on without thought ? Could the 
spinal cord carry on reflexes without the brain ? If nothing 
disturbed the outer ends of the afferent nerves, would a reflex 
center ever cause movement ? Think out these problems, and 
you will read the next paragraphs more intelligently. 












THE NERVOUS SYSTEM 


219 


MUSCLE CELL 


DING OF 
NERVE FIBER IN 
MUSCLE CELL 


The Spinal Cord as a Reflex Center. The spinal cord can 
carry on reflexes in a wonderful way without the aid of the 
brain. A shark with its head cut off, swims in a very natural 
manner. A turtle can walk about after it has lost its head. 
If a drop of weak acid or strong vinegar is put on the back 
of a brainless frog, the frog 
will wipe the acid or vinegar 
off with its foot. If the foot 
that the frog is using is held, 
the other foot will then be used. 

The spinal cord, without the 
brain, can carry on reflex ac¬ 
tions for any part of the body 
that is supplied by the spinal 
nerves. 

What the Spinal Cord does 
in Reflexes. The spinal cord 
not only acts as a connector 
between the afferent and the 
efferent neurons, but it makes 
the right connections so that 
the proper muscles will be -, ¥ „ 

^ r FIG. 102. The efferent nerve ending 

moved. It also arranges and in the voluntary muscle cells. Through 

sets in order the impulses that the nerve fibers im P ulses come into the 

muscle cells and cause them to contract. 

come to it, hurrying them on to 

some muscles, holding them back from others, making some of 
the stimuli strong and others weak, so that in a movement like 
the swimming of the shark, which involves almost the whole 
body, each muscle gets its stimulus so that it will contract at 
exactly the right moment and with the proper force. Yet 
the spinal cord has no intelligence; for a brainless frog will 
sit and dry up beside the water that would save its life, and 




220 


HUMAN PHYSIOLOGY 


all memory is gone from an animal that has only a spinal 
cord. 

Other Reflex Actions. Reflex centers are found not only 
in the cord but also in the medulla and in the lower part of 
the brain in front of the medulla, and to a large extent the 
body is governed through its reflex centers. If the eye is 
touched, the eyelids will close. Tickling the inside of the 
nose causes sneezing, and tickling the inside of* the larynx 
causes coughing. Cold water thrown on the face causes the 
breath to be drawn in suddenly, while a sharp odor, as of 
ammonia, stops the inspiration. Water starting into the nose 
also checks the breath, and in diving birds, water poured 
across the nostrils will for a long time hinder inspiration. 
Heat on the skin makes the vessels relax, and cold causes 
them to contract. The passing of digested food into the 
intestine causes the pancreas to secrete its juice and the gall 
bladder to be emptied. Almost the entire government of 
the internal organs is carried on by reflexes of which we are 
not even conscious, but when one of these organs gets into 
trouble, the impulses that the afferent nerves carry up to the 
brain give us the sensation of pain and let us know that some 
of our organs need attention. 

The Body Self-governing through the Reflexes. A close 
study of the reflexes shows that they are all purposeful. 
Even those which are carried out without intelligence or con¬ 
sciousness are all beneficial to the body. In studying them, 
one also becomes impressed with the fact that the body itself 
brings these reflexes about, and through them largely regu¬ 
lates itself. For example, when the heart beats hard and the 
arteries are tightly stretched with blood, it takes a forcible 
contraction to squeeze the blood out of the ventricles into the 
arteries. The pressure of the blood within the heart then 


THE NERVOUS SYSTEM 


221 


starts impulses up the afferent nerves of the lining of the 
heart. These pass to the medulla, and impulses which slow 
up the beat of the heart come down the efferent nerves. 
Thus the heart largely regulates itself, the high blood pres¬ 
sure causing it to slow its beat. By the effects of heat and 
cold on the skin, the blood vessels are largely controlled, and 
many other parts of the body are also, to a certain extent, self- 
governing. We must not give too much credit to the nervous 
system for its wonderful wisdom in regulating the body, for 
usually the impulses which cause the action of the muscles 
and glands are not started by the nervous system at all, but 
by some other part of the body, and all that the nervous sys¬ 
tem does is to make the proper connections between the 
afferent and efferent nerves. 

Acquired Reflexes. Besides these natural reflexes, there 
is another set of reflexes that is acquired by practice. In 
skating, riding a bicycle, rowing, boxing, fencing, playing a 
piano, and in almost any kind of activity, movements are 
made without thought. The eye of the piano player sees a 
certain note, and his finger strikes the right key. The bicycle 
rider feels a slight leaning of his wheel to the side, and he 
shifts his body so as to keep the balance. These movements 
have been made so often that they become reflex, and are 
carried out without thought. 1 

Habit. The performance of any act with which the mind 
is connected makes easier a further performance of that act. 
For instance, the fingers of the pianist move slowly and awk¬ 
wardly at first, since the mind requires time to decide where 

1 The acquired reflexes are all associated with the mind, and their seat is in 
the outer layer of the cerebrum. When this is removed, all the acquired reflexes 
are lost, while the natural reflexes that are carried on by the lower parts of the 
brain and by the cord remain. 


222 


HUMAN PHYSIOLOGY 


each finger shall be placed. But after long practice the 
fingers move rapidly and without thought. By practice the 
skilled swordsman has trained his nervous system so that 
without thought — so quickly that there is not time for 
thought — his sword follows that of his antagonist and turns 
aside the thrust. 

As a physical habit can be formed by the repetition of an 
act, so mental and moral habits can be formed — habits of 
good work and of poor work; of honesty and dishonesty; of 
neatness and accuracy, and of carelessness and untidiness; 
habits of preparing lessons and of leaving them unprepared. 
All kinds of habits are formed most readily in youth, and 
it is seldom that, after the age of twenty-five or thirty, long- 
established habits are broken. Indeed, it is difficult at any 
time of life to break a habit that has once been thoroughly 
formed. The pupil who is idle in the third grade is usually 
an idler still in the sixth grade. The triffer in the sixth grade 
is usually a trifler still in the high school; and it would be 
almost a miracle to find a high school drone who had become 
a capable and industrious college student. 

Just what it is in the nervous system that makes it want 
to keep doing the same things over again, is not known. But 
it is well known that what a person does in youth determines 
very largely what that person will both do and be in his later 
life. The character is largely formed by the habits, and there 
is much truth in the old proverb which says, “ Sow an act 
and reap a habit; sow a habit and reap a character.” 

Summary. The nervous system controls the body and is 
the organ of the mind. 

Most of the nerve cells are in the brain and spinal cord, but 
a few of them are in ganglia. A nerve cell and its fiber are 
called a neuron. Nerve fibers that carry impulses outward 


THE NERVOUS SYSTEM 


223 


are efferent fibers, and those that carry them inward are 
afferent fibers. The nervous system does a great part of 
its work by acting as a connector of the body parts. It is 
arranged like a telephone system in which the spinal cord 
and brain correspond to the central office. 

The cerebrum is the largest division of the brain. It is 
divided into hemispheres and has many convolutions on its sur¬ 
face, to give room for the cells that are associated with the mind. 
The fibers from it cross in the medulla, so that the two hemi¬ 
spheres of the cerebrum are connected with opposite sides of 
the body. The cerebrum is the seat of the mind and of the 
sensations, and originates impulses that cause voluntary motion. 

The cerebellum causes the muscles to keep a proper amount 
of contraction and coordinates the movements of the muscles 
of locomotion. The pons is a bridge between the different 
parts of the brain. The medulla connects the brain and spinal 
cord and gives rise to nerves that supply the head and many 
internal organs, including the heart and lungs. The function 
of the medulla is to transmit stimuli and act as a reflex center. 
The spinal cord gives rise to many nerves. It conducts 
stimuli and is a reflex center. 

In a reflex action the impulse starts in an afferent nerve, 
passes inward to the brain or cord, and comes out again along 
an efferent nerve. Reflexes are carried on without thought, 
and through them the body is in a great measure self-regu¬ 
lating. Certain reflexes may be acquired by practice, and 
habits are easily formed. To a large extent the habits formed 
in youth determine what the character will be. 

QUESTIONS 

Give two functions of the nervous system. Where are most of the 
nerve cells found? What is a ganglion? an axis cylinder? a neuron? 


224 


HUMAN- PHYSIOLOGY 


What is an afferent nerve fiber? an efferent nerve fiber? How is 
an important part of the work of governing the body done by the 
nervous system? What is the advantage in having the nervous 
system arranged with a central portion through which all the body 
parts are connected ? 

What are the parts of the central nervous system? How large is 
the brain as compared with the spinal cord? Name the three 
divisions of the brain. How large is the cerebrum? How is it 
divided? What are the convolutions? Where is the gray matter of 
the cerebrum? Of what is it composed? With what is it as¬ 
sociated? With what part of the body is the right hemisphere of 
the cerebrum connected? Where do the fibers from the cerebrum 
cross? Give three functions of the cerebrum. 

What is the arbor vitae? Give two functions of the cerebellum. 
What is the result of injury to the cerebellum? Where is the pons? 
Of what is it composed and what does it do? What part of the body 
is supplied with nerves from the medulla? Why does injury to the 
medulla cause death ? Give two functions of the medulla. 

Where are the fibers in the spinal cord? the cells? What two 
functions has the cord? What is a reflex action? Give an example 
of one. What is the great function of the spinal cord in a reflex 
action ? 

Mention some reflexes that can be carried on without the brain. 
What does the spinal cord do in these reflexes in addition to making 
the connections? Does it have intelligence? Where are some 
other reflex centers? What are some of the reflexes that are carried 
on by them? Give some examples of how the body regulates itself 
through reflexes. 

What is an acquired reflex? Give examples of acquired reflexes. 
How are habits formed? Why is it important that correct habits be 
formed early in life? 


CHAPTER XVII 

THE NERVOUS SYSTEM (Continued) 


NERVES 


The Cranial Nerves. The twelve pairs of cranial nerves 
rise from the brain. The first pair are the nerves of smell, 
and the second pair are the nerves of sight. The nerves of 
taste and of hear¬ 



ing are also cra¬ 
nial nerves. In 
general, the cra¬ 
nial nerves sup¬ 
ply the head, 
but one pair of 


Fig. 103. The spinal cord and the roots of a pair of spinal 
nerves. 


nerves from the medulla goes to the internal organs of the 
body (page 216). 

Spinal Nerves. Thirty-one pairs of spinal nerves pass out¬ 
ward from the spinal cord through openings between the 
vertebrae. Each spinal nerve has a ventral and dorsal set of 
roots. The ventral roots come from the front of the cord and 
the dorsal roots from the back of the cord. The ventral 
roots contain the efferent fibers, and the dorsal roots the 
afferent fibers. Outside of the spinal column the roots unite 
to form one nerve, which contains both efferent and afferent 
fibers. 

Effect of cutting and stimulating a Spinal Nerve. The affer¬ 
ent impulses pass into the cord through the dorsal roots of a 












226 


HUMAIV PHYSIOLOGY 


spinal nerve; the efferent impulses pass out of the cord 
through the ventral roots. What effect would it haVe on the 
part that is supplied by a spinal nerve, if the nerve were 
cut as in A (Fig. 104)? If it were cut as in B ? as in C ? 



Fig. 104. A is a spinal nerve that has been cut; B is a spinal nerve, with the 
efferent root cut; C is a spinal nerve with the afferent root cut. 

A nerve impulse started in the wrong direction in a nerve 
produces no effect. Suppose that by pinching the cut end 
of the nerve or by touching it with an electric wire you stimu¬ 
lated it and started an impulse in it. What effect would it 
have to stimulate the cut end at a (Fig. 104)? at b ? at cl 
at d ? at e ? at fl 

'X 

THE SYMPATHETIC NERVOUS SYSTEM 

Nearly all the cells of the central nervous system are in the 
brain and spinal cord. They are collected in great centers. 
The cells of the sympathetic nervous system are in ganglia, 
which are scattered through the body. This system consists 
chiefly of two chains of ganglia, one on either side of the 
spinal column ; of scattered ganglia in many of the internal 
organs, especially the intestine and other abdominal organs; 
of a great network of fibers that connect all these ganglia 
with each other and with the spinal cord and brain ; and of 
the sympathetic nerves that supply various organs. 

From some of the cranial nerves and from all of the spinal 
nerves, branches run to and from the sympathetic ganglia. 
Every part of the sympathetic nervous system is thus con- 


THE NERVOUS SYSTEM 


227 


nected with the central nervous system, the 
medulla and the sympathetic system being 
especially closely connected. Thus the central 
nervous system is able, through the sympa¬ 
thetic system, to reach the parts of the body 
that are not supplied with nerves directly from 
the brain and cord. 

The Function of the Sympathetic System. In 

general the sympathetic system controls the in¬ 
ternal organs (heart 
and blood vessels, di¬ 
gestive organs, kid¬ 
neys, etc.) and the 
sweat glands and ves¬ 
sels of the skin. It 
controls these organs 
chiefly through reflex 
actions, yet the 
sympathetic system is 
not an independent 
system. It cannot do 
its work without the 
central nervous sys¬ 
tem, as you will un¬ 
derstand when you 
have learned how 
sympathetic reflexes 
are carried out. 

Sympathetic Re- 


_ FROM MEDULLA 
HEART, LUNGS. AND 
STOMACH 





Fig. 105. The 
two chains of 
sympathetic gan¬ 
glia. 


Fig. 106. Side view of the sym¬ 
pathetic nervous system. Note the 
chain of ganglia Iving beside the flexes. A sympathetic ganglion 
spinal golumn, and the great net- j ms nQt ^ p ower f 0 fum an impulse 


work of fibers running to the in¬ 
ternal organs. 


back and cause a reflex action, but 










228 


HUMAN- PHYSIOLOGY 


when the ganglion receives an afferent impulse, it sends the 
impulse on into the spinal cord or brain, where it is started 
back down an efferent nerve. The impulses go through 
ganglia on their way to and from the cord and brain, 
but the reflex centers lie in the central system. Although 
the central nervous system takes part in the sympathetic 
reflexes, yet we have no consciousness of these reflexes. 
Neither is it possible for us by a voluntary effort to 
influence the internal organs through the sympathetic sys¬ 
tem. This system is connected with the spinal cord and with 
the lower centers of the brain, and not with the higher cen¬ 
ters of the brain, with which the mind is associated. 



Fig. 107. In the sympathetic system the nerve impulses pass through ganglia on 
their way to and from the cord and brain. 


The Sympathetic a Part of the Central Nervous System. 

The entire nervous system works together in governing the 
body, and it gives a wrong impression to speak of two 
systems. The sympathetic is, after all, only a branch of 
the central nervous system that is ruled without our knowl¬ 
edge by the cord and by the lower centers of the brain. 
It contains such a network of fibers that almost all the 
internal parts of the body are connected the one with the 
other, so that it is impossible for one of these organs to 
become deranged without affecting the other organs. The 
organs thus “ sympathize” with each other, and for this reason 
the nerves to these parts are called the sympathetic system 





THE NERVOUS SYSTEM 


229 


THE NERVOUS SYSTEMS OF OTHER ANIMALS 


The great difference in the nervous systems of the higher 
and lower vertebrates is in the cerebrum. In the lower 
forms, as in the fishes, frogs, and 
reptiles, the cerebrum is small 
and smooth, and contains on its 
surface only a few of the nerve 
cells (gray matter) that in man 
are associated with the mind. 

In the higher animals, the cere¬ 
brum is greatly increased in 
size, and its surface becomes 
convoluted, making room for a 
great number of nerve cells on 
its surface. As a general state¬ 
ment, it is true that intelligence 
increases with the development 
of the cerebrum. The lower forms with small cerebrums are 
stupid, and higher animals with larger and more convoluted 
cerebrums are more intelligent. The cerebrum of man is the 
most highly developed of all, and man is the most intelligent 
of all animals. 



Fig. 108. The brain of a snake (A), 
and of a cat ( B ). 


HYGIENE OF THE NERVOUS SYSTEM 

The nervous system is so closely connected with all parts of 
the body that it is of the utmost importance to keep it in 
health. Good food and fresh air are necessary to the nerve 
cells, as they are to all other cells. In the special hygiene of 
the nervous system, the following points should be noted : 

Sleep. Sleep is absolutely necessary to the nervous sys¬ 
tem. During sleep the nerve cells rest and prepare them- 





230 


HUMAN PHYSIOLOGY 


selves for further work, and the idea that it is possible to 
sleep too much is probably incorrect. Babies should sleep 
from fifteen to twenty hours out of the twenty-four, older 
children from ten to fourteen hours, and adults from seven to 
ten hours. Occasionally a person is found who keeps in good 
health on five or six hours of sleep, and other persons are 
found who must have eleven or twelve hours. Most people 
under twenty years of age are better off with ten hours of 
sleep than with eight or nine hours, and most older persons 
keep in better health when they sleep nine full hours than 
when they sleep seven or eight hours. 

There is no surer way to undermine the health than to stay 
up late at night and get up early in the morning, thus cutting 
short the hours of sleep. One who is doing this may think 
he is in good health, but if he will enter an athletic contest or 
do something else that will really put his nervous system to 
the test, he will find that he is not in the best condition. A 
runner who has been losing sleep has not the slightest chance 
of winning from others who have had long and regular hours 
of sleep. His nervous system cannot control his muscles 
quickly and accurately enough to prevent his falling behind 
in the race. 

Tobacco. The evil effects of tobacco on the nervous system 
are generally recognized. Its weakening effect on the mus¬ 
cles has already been noted (page 74), and it seems to produce 
this effect more by interfering with the nervous regulation of 
the muscles than by injuring the muscle cells themselves. 

Persons who use tobacco are often troubled with a restless¬ 
ness and a jerkiness of movement, so that they cannot remain 
long in any one position. They are also subject to more or 
less constant trembling of the extremities, especially of the 
hands. Men who use tobacco seldom have the steadiness of 


THE NERVOUS SYSTEM 


231 


nerve required to make expert marksmen, and athletes who 
are training for contests of strength, endurance, or skill are 
not allowed to use tobacco in any form. 

The effects of tobacco on the mind are more pronounced 
than its effects on the nervous control of the muscles. One 
class at Yale University was divided into four grades accord¬ 
ing to scholarship. ‘Only 25 per cent of those in the highest 
division used tobacco, while 85 per cent of those in the lowest 
division were tobacco users. In another class 90 per cent of 
the first honor men were non-users of tobacco. 

In young pupils the effects of tobacco on the mind are 
much more marked than are its effects in older persons. In a 
Chicago school, out of 125 boys who smoked, only two were 
able to keep up with their class. Nine tenths of these 125 
boys belonged to educated, intelligent families; they had 
been given excellent school advantages; yet among them 
were found nearly all the boys who were from two to four 
years older than the average age of the children in their 
grade. In all, there were reported in Chicago 2402 pupils 
who were cigarette smokers, and only 6 per cent of them 
were able to do the school work of their grade. It is reason¬ 
able to believe that the use of tobacco had dulled the minds of 
these boys and had changed many of them from bright, 
active pupils into idling incompetents. 

Tobacco also often leads to moral degeneration. Nothing 
is more fatal to ambition than tobacco, and to an extent it 
destroys the will power. A boy begins smoking a few cigar¬ 
ettes, and soon the habit has fastened itself on him so firmly 
and his will has been so weakened that he cannot break the 
habit, even when he realizes that he is injuring himself. The 
great majority of boys who smoke cigarettes are irritable, per¬ 
verse, and careless of the rights of others. Our prisons and 


232 


HUMAN" PHYSIOLOGY 


reformatories are filled with those who began smoking cigar¬ 
ettes in youth. What would have been the fate of each of 
these persons if he had not used tobacco, is of course im¬ 
possible to say; but there is no doubt but that many of 
them would have led successful lives if it had not been for 
cigarettes. 

So well known are the effects of tobacco on the young, that 
in nearly all our states and in many foreign countries, stringent 
laws have been passed making it a crime to sell or give 
tobacco to boys under a certain age. One state has even 
prohibited the use of cigarettes in any form by old or young. 



Fig. 109. At the left is a healthy nerve cell from a sympathetic ganglion. The 
others are nerve cells from one of the sympathetic ganglia of a man who died of alco¬ 
holic paralysis. Note the breaking down of the cells that the alcohol has caused. 


Employers often favor those who do not use tobacco, and 
many employers will have nothing to do with tobacco-using 
boys. The evil effects of tobacco are known to the world, 
and this evil effect falls most heavily on the nervous system. 

Alcohol. To tell the exact effect of a very small amount 
of alcohol on the nervous system is no more possible than to 
tell the exact effect of a small amount of alcohol on any 
other part of the body. When any considerable amounts of 
alcohol are taken, however, the entire nervous system is 
deranged. The following effects are very noticeable when 
alcohol is used to excess : 

If enough alcohol is given to an animal to produce intoxi- 


THE NEE VO(/S SYSTEM 


233 


cation, in from ten to forty minutes the branches of some of 
the nerve cells will be found to be shrunken and gathered 
into little knots, and certain granules that are found in the 
protoplasm of nerve cells will have broken down. In long- 
continued excessive use of alcohol, many of the cells die, and 
it is also common for nerve fibers to degenerate and die, 
causing paralysis. Continued use of alcohol also causes a 
thickening of the connective-tissue membranes of the brain, 
and of the supporting tissue within the gray matter of the 
brain, so that the brain of a confirmed alcoholic contains 
fewer nerve cells and more supporting tissue than does a 
normal brain. In delirium tremens, some changes that are 
not at all understood occur in the nerve cells generally. 
With such changes in structure of the nervous tissue, we 
should naturally expect the great disturbances of function 
which alcohol causes. 

Almost every one is familiar with the way the nervous 
system loses control of the muscles when it is under the in¬ 
fluence of alcohol. The weakening of the muscles that fol¬ 
lows the use of alcohol (page 74) seems to be due more to 
its effect on the nervous system than to the effect on the 
muscles themselves. The nervous system is as greatly in¬ 
fluenced by alcohol in its other work, as in its work of regu¬ 
lating the muscles; the mind of an intoxicated person works 
no more accurately than his muscles work. Drunkenness 
may very properly be considered as temporary insanity, 
caused by the poisoning of the nerve cells by alcohol. De¬ 
lirium tremens is a condition in which the cells have been so 
repeatedly poisoned that ideas are associated in the most 
grotesque and frequently terrifying manner. 

The effects of alcohol on animals are very marked. Kittens 
that were daily intoxicated with alcohol lost all interest in 


234 


HUMAN PHYSIOLOGY 



FlG. iio. These are normal kittens, and they are playing as healthy kittens do. 


play, cleanliness, and mice, and showed no fear of dogs. 
They ate and slept, but took no interest in anything else, 
acting strikingly like animals from which the cerebrum had 
been removed. Dogs that had been given alcohol daily in 
moderate amounts showed the most extreme fear, howling 



Fig. hi. These kittens have been given alcohol. They are stupid and sleepy, 
dnd have lost all interest in play. (From a photograph by Pr. G. F, Hodge.) 










THE NERVOUS SYSTEM 


235 


and cringing when a bell was rung or when the floor was 
struck, and awakening from their sleep to cower in terror or 
run and howl in an agony of causeless fear. This timidity 
continued after the giving of alcohol had been stopped, show¬ 
ing that the mental workings of the brain had been perma¬ 
nently injured. 

The results of these experiments show the very great effect 
of alcohol on the mind. It is estimated that 20 per cent of 
insanity comes from this cause, and it is proper to conclude 
that just as alcohol injures the liver and kidneys, so it injures 
the nerve tissue; and as it interferes with the workings of 
the liver and kidneys, so it interferes with the function of the 
nervous system, both in governing the body and in its work 
as an organ of the mind. 

Summary. The twelve pairs of cranial nerves rise from 
the brain. They supply the head and many of the internal 
organs. The thirty-one pairs of spinal nerves rise in the 
spinal cord. Each nerve has a set of ventral roots that con¬ 
tain the efferent fibers and a set of dorsal roots that contain 
the afferent fibers. 

The sympathetic nervous system consists of a network 
of ganglia and fibers. It controls by reflexes the internal 
organs, the blood vessels, and the sweat glands. It is con¬ 
nected with the central nervous system and cannot carry on 
its work alone. It is called the sympathetic system because 
by it all the internal organs are connected and through it 
they “ sympathize ” with each other. 

Intelligence increases with the development of the cere¬ 
brum. The lower vertebrates have small, smooth cerebrums 
and the higher vertebrates have larger and more convoluted 
cerebrums. The human cerebrum is the most highly devel¬ 
oped of all. 


2 36 


HUMAN PHYSIOLOGY 


Because the nervous system is directly connected with all 
parts of the body, it is very important to keep it in health. 
The special need of the nervous system is sleep, without 
enough of which we cannot have good health. 

Tobacco interferes with the nervous control of the muscles. 
It also dulls the mind. It is especially harmful to the young, 
as is shown by the fact that only 6 per cent of 2402 cigarette 
smokers in the Chicago public schools were able to do their 
school work. Another effect of tobacco is a weakening of 
the moral nature. 

Alcohol affects the structure of nerve tissue, the excessive 
use of alcohol causing many of the nerve cells and fibers to 
die. It also affects the function of nerve tissue, intoxication 
causing the nervous system to lose its control of the muscles 
and its mental power. The minds of animals are perma¬ 
nently injured by alcohol, and among human beings about 
20 per cent of insanity is caused by it. 


QUESTIONS 

How many pairs of cranial nerves are there? Where do they rise? 
What part of the body do they supply? 

How many pairs of spinal nerves are there? Where do they rise? 
What kind of fibers are in the dorsal roots ? the ventral roots ? 

Of what does the sympathetic nervous system consist? How is the 
central nervous system connected with it? What part of the body 
does it control? Explain how a sympathetic reflex is carried out. 
Are we conscious of these reflexes? Can we control them? Why is 
this part of the nervous system called the sympathetic system ? 

What is the great difference in the nervous systems of the higher 
and lower vertebrates? What increases with the development of the 
cerebrum ? 


THE NERVOUS SYSTEM 


23 7 


How much sleep is needed by persons of different ages ? What is 
said of the importance of sleep? 

What effect has tobacco on the muscles? How does it produce 
this effect? What did investigations at Yale University show in 
regard to the effects of tobacco on the students? How many of the 
125 cigarette smokers in one Chicago public school kept up their 
school work? What per cent of the cigarette smokers in all the 
schools investigated did so? What effect has tobacco on the am¬ 
bition? on the will power? As a rule, are cigarette smokers worried 
about their own condition and anxious to do better? Why have laws 
been made against selling cigarettes? Why do employers favor boys 
who do not use tobacco? 

What is the effect on the nerve cells of an animal of sufficient alco¬ 
hol to cause intoxication? How quickly does it produce this effect? 
What effect has long-continued and excessive use of alcohol on nerve 
tissue ? on the supporting tissue of the brain ? What effect has alcohol 
on the nervous control of the muscles? on the mental workings of the 
nervous system? 

What effect had daily intoxication on kittens? What effect had 
moderate amounts of alcohol on the minds of dogs? 


A reflex movement (Fig. 101) is quicker than the movement 
would be if the impulse had to go to the brain. Explain why. What 
advantage is there in having the body governed by reflexes that 
require no attention from the mind? 

When the “ funny bone ” is struck, a nerve in the arm is crushed 
against the bone. What part of the body is affected? Explain why. 
Persons who have had a limb amputated sometimes complain of 
pain in the lirilb. What causes this sensation? Where is the 
trouble in a paralytic stroke ? 



CHAPTER XVIII 

THE EFFECTS OF ALCOHOL ON THE HUMAN BODY 


The question of the use of alcoholic drinks is one that con¬ 
tinually agitates our nation, and indeed has been receiving, 
for many years, the serious attention of the whole civilized 
world. The opponents of alcohol insist that it is the chief 
cause of poverty and crime, and they urge against alcohol 
the physiological argument that it injures the body. Other 
persons maintain that alcohol, in moderate quantities, is 
beneficial to the body. 

We have already learned something of the effects of alcohol 
on many of the different organs of the body. The human 
body, however, is more than a collection of organs. It is 
one whole, and any physiological question must be looked at 
from the standpoint of the body as a whole. In this chapter 
we shall take up the effects of alcohol on the body from a 
more general view point. 

What is Alcohol ? Alcohol is a substance formed from 
sugar by a small plant called 
yeast. When yeast grows in 
water in which sugar is dissolved, 
it digests or ferments the sugar, 
breaking it up into water, carbon 
dioxid, and alcohol. The alcohol, 
like the carbon dioxid, is poisonous to the yeast if present in 
large quantities. 

Alcoholic Drinks. The most common alcoholic drinks are 
wine, cider, beer, and distilled liquors. Wine and cider are 

238 



Fig. 112. Yeast plants. 


EFFECTS OF ALCOHOL ON THE HUMAN BODY 239 


made by allowing yeast to ferment the sugar in fruit juice. 
If it is apple juice that is fermented, the product is cider. If 
grape juice is fermented, the product is wine. Beer is made 
by allowing the yeast to ferment sugar from grain. The 
starch in the grain is first changed to sugar by sprouting 
the grain, after which it is ready to be fermented by the yeast. 1 

Brandy is manufactured by distilling fermented fruit juice. 
Whisky is made by distilling the fermented material from 
grain or potatoes, and rum by distilling fermented molasses. 
Beer contains on an average about 5 per cent of alcohol, 
wine contains about 10 per cent of alcohol, and distilled 
liquors contain about 50 per cent of alcohol. 

Alcohol and Length of Life. If alcohol as it is commonly 
used is beneficial to the body, drinkers should live longer 
than those who abstain from alcohol. If alcohol injures the 
body, we should expect abstainers to be longer lived than 
drinkers. The best possible way, therefore, of settling the 
question as to whether alcohol injures or benefits the body is 
to compare the death rates of drinkers and of abstainers. 

The United Kingdom Temperance and General Provident 
Institution is a life insurance company of London, England. 
For more than fifty years this company has kept separate 
lists of the moderate 2 drinkers and abstainers among its policy 

1 In distilling liquors, the liquid (the fruit juice or the water in whicf* the 
grain has been soaked) that contains the fermented sugar is heated, and t£e 
vapor that comes from it is caught and condensed. The alcohol in the liquid is 
changed to vapor more easily than the water, and the liquors that are manufac¬ 
tured in this way are strong in alcohol. 

2 All insurance companies refuse to accept heavy drinkers, and they reject 
many persons who are very moderate drinkers indeed. The above statistics, 
therefore, apply only to those .who were moderate drinkers at the time they were 
insured. Some of them may later have become excessive drinkers, but if all 
drinkers were included in the statistics, the death rate among the alcohol users 
would be very much higher than is here shown. 


240 


HUMAN PHYSIOLOGY 


holders. Its records show that for every 74.3 deaths among 
abstainers, there are 100.4 deaths among the drinkers. The 
death rate is, therefore, 35 per cent higher among the 
users than among the non-users of alcohol. Many other life 
insurance companies have kept similar records, and in every 
case the death rate is from 25 to 50 per cent higher 
among the drinkers than among the abstainers. These 
averages have been made up from records including many 
thousands of lives, and there is no doubt of their correct¬ 
ness. They have been examined with great care to see 
if there was any reason other than the use of alcohol why 
the drinking man should die earlier than the non-drinker. 
No such reason can be found, and it is certain that the 
users of alcohol fail to live as long as those who do not use 
alcohol, because the alcohol weakens and injures the body. 1 

Alcohol and Tuberculosis. We have already seen (page 171) 
that alcohol lowers the power of the body to resist disease 
germs. The relation of alcohol to tuberculosis deserves 
special mention. 

In France, the districts drinking 12.5 liters of wine per capita 
had annually 3.3 deaths from tuberculosis for each one thou¬ 
sand inhabitants. The districts drinking 35.4 liters of wine per 
capita had annually 10.8 deaths from tuberculosis for each one 
thousand inhabitants. In the sanatoria for consumptives at 
Loslau, Germany, in 1899, 30 per cent of the patients were 
avowed alcoholics, 37 per cent were moderate drinkers, 27 per 
cent were occasional drinkers, and only 6 per cent were total ab¬ 
stainers. According to estimates made in France, 10.3 per cent 
of the children of drunkards suffer from tuberculosis, while only 
1.8 per cent of the children of total abstainers have tuberculosis. 

1 A German society offers a reward of one thousand marks to any one who 
will prove the incorrectness of the figures that have led to this conclusion. 


EFFECTS OF ALCOHOL ON THE HUMAN BODY 241 

Statistics like these show clearly that alcohol users are 
especially subject to tuberculosis. So thoroughly established 
and so important is this fact, that in Paris, in 1905, the Inter¬ 
national Tuberculosis Congress, whose members include the 
most learned bacteriologists and physicians in all the world, 
adopted the following resolution: “We strongly emphasize 
the necessity and importance of combining the fight against 
tuberculosis with the struggle against alcoholism.” 

The Relation of Alcohol to Insanity. The great increase in 
recent years of the number of the insane has excited alarm, 
and considerable time has been devoted to studying the causes 
of insanity. From a careful study of the causes bringing on 
insanity in the patients in all the asylums in England, Wales, 
and Ireland, it is estimated that alcohol causes about 20 
per cent of all insanity. In England, personal intemperance 
(intemperance of the insane person himself) causes nearly 
15 per cent of insanity, and intemperance of the parents 
causes enough more to bring the total to about 20 per cent. 
When one thinks of the very great effect that alcohol has on 
nerve tissue, and of the way it affects the working of the 
mind, it does not seem at all strange that continued drinking 
should bring on insanity. 

Alcohol and Heredity. Whether or not the children of 
those using alcohol are affected by the drinking of their par¬ 
ents is a question that cannot be neglected. That children 
are very greatly affected by drunkenness in their parents, the 
following facts make certain: 

Two pairs of dogs, as nearly alike as possible, were selected. 
One pair was given alcohol in their food, and the other pair 
had the same food and care, without alcohol. Of twenty- 
three puppies of the pair of dogs that had alcohol, nine were 
deformed, ten were born dead, and only four lived. The 


HUMAN PHYSIOLOGY 


242 

other pair of dogs in the same time raised forty-five puppies, 
four of which were deformed and forty-one of which lived. 
Thus, only 17.4 per cent of the puppies born to the alcoholic 
dogs lived, while 90.2 per cent of the much larger number 
born to the other dogs lived. 

Much the same effect is produced in human families by 
alcohol. In ten alcoholic families investigated, there were fifty- 
seven children. Of these children, ten were deformed, six 
were idiots, six were epileptics, twentydive failed to live, and 
only ten of the fifty-seven, or 17 per cent, were normal 
and healthy. In ten families not using alcohol that were in¬ 
vestigated, there were sixty-one children. Of these, two were 
deformed, five failed to live, and fifty-four, or 88.5 per cent, 
were normal and healthy. One investigator estimates that 
only about 17.5 per cent of the children of drunkards are 
physically sound; another places the percentage at 11.7 per 
cent; and still another reports that of the children of drunken 
parents examined by him, not more than 6.2 per cent were 
strong and well. These facts show that the bodies of children 
are affected by the intemperance of their parents. 

The minds of children are also affected by the drinking of 
parents, as the following facts show: 

Of 8624 children of drunken parents, 53 per cent were 
mentally defective, while of 13,323 children of sober parents, 
only 10.1 per cent were unable to keep up with their school 
work. Of children whose ancestors had been free from 
alcoholic taint for three generations, 96 per cent were pro¬ 
ficient in school work, while of those who had three gen¬ 
erations of alcoholic ancestors, only 23 per cent were able to 
keep up with their classes, and 76 per cent had some 
nervous trouble. 

We thus see that the evil effects of alcohol on both mind 


EFFECTS OF ALCOHOL ON THE HUMAN BODY 243 


and body are inherited. Professor Welch of Johns Hopkins 
University says, “ The brunt of the evil heritage of alcohol 
falls on the nervous system of the second generation.” 

Alcohol and Character. The relation of the body to the 
mind is not understood. We do not know, therefore, how 
drugs affect the mind and character of a person, but we do 
know that drugs can do this. The continued use of opium 
will change an upright and honorable person into a shameless 
falsifier. Cocaine sometimes turns mere boys into desperate 
criminals, who do not shrink from robbery and murder. 
Alcohol also has a great effect on the character. By intoxi¬ 
cation, some mild and kind men are changed into cruel and 
dangerous persons, and the breaking down of the will power 
and character in confirmed drunkards is something with 
which many people are familiar. 

The following facts show that, in the opinion of business 
men, drinking renders men on the whole less faithful, honest, 
and efficient. Bonding companies are suspicious of drinking 
men, and often refuse to furnish bonds for men who frequent 
saloons. The Fifth Avenue National Bank of New York 
City has for thirty years forbidden even its clerks and mes¬ 
senger boys to drink in saloons and barrooms. Many large 
railroads refuse to employ drinking men in their operating 
departments, and some of them refuse to employ drinkers 
even as bookkeepers or ticket agents. Shrewd business 
men everywhere, in employing men, give the preference to 
abstainers over drinkers. Any young man seeking employ¬ 
ment in a responsible position will soon learn that one of 
the first questions asked an applicant is whether or not he 
drinks. 

Conclusion. We find that alcohol shortens life; that it 
makes the users of it more susceptible to germ diseases, thq 


244 


HUMAN PHYSIOLOGY 


relation of alcohol drinking to tuberculosis showing this in 
a striking way; that alcohol causes a considerable amount of 
insanity, and that the drinking of parents has a very inju¬ 
rious effect on the bodies and minds of their children. We 
also find that alcohol has a tendency to destroy the will 
power and the character of those who use it. 

These are facts that must be faced by any one investi¬ 
gating the effects of alcohol on the human body. The only 
answer that can be made to these facts is that it is the abuse 
and not the use of alcohol that works all this evil. This is a 
question that need not be discussed here, for practically every 
one who uses alcohol at all uses too much of it (page .131). 
When it is used as mankind uses it, its effects are the evil 
effects given above. 


QUESTIONS 

How is alcohol formed? What is cider? wine? beer? How are 
distilled liquors manufactured? How much alcohol is in wine? in 
beer? in distilled liquors? 

What figures are given as to the death rates of drinkers and 
abstainers? Why must these figures be regarded as reliable? 

What reasons are there for thinking that in France wine drinkers 
are especially subject to tuberculosis? What facts from Germany 
indicate that alcohol increases consumption? What effect has 
alcohol drinking on the amount of tuberculosis among the children 
of the drinkers? What is the opinion of the International Tuberculosis 
Congress in regard to the connection between alcoholism and 
tuberculosis ? 

What per cent of insanity, according to estimates made in England, 
is due to alcohol? Tell something of the effects of alcohol on the 
children of the drinkers. What effect does alcohol often have 
on the character? What facts show that business men consider 
alcohol users less trustworthy than non-drinkers? 


CHAPTER XIX 


THE SPECIAL SENSES : Touch, Taste, Smell, and Hearing 

Part of the nerve impulses that are carried into the brain 
cause reflex actions; part of them cause sensations. It is 
difficult to describe a sensation, but we have all experienced 
sensations of light, sound, touch, heat, cold, and hunger. 
There is, therefore, no difficulty in understanding the mean¬ 
ing of the term. 

General Sensations. Hunger is caused by afferent im¬ 
pulses from the stomach, and thirst by impulses from the 
pharynx. Afferent impulses from the muscles (for every 
muscle has great numbers of afferent as well as efferent nerve 
fibers ending in it) cause the sensation of tiredness, and other 
impulses give rise to feelings of pain, nausea, and other sen¬ 
sations. These impulses rise within the body ; they originate 
because of some condition of the body, and they cause what 
are called the general sensations. Most (but not all) of the 
general sensations are caused by impulses that come from all 
parts of the body. 

Special Sense Organs. In some parts of the body are 
special sense organs. In these the afferent nerve fibers end 
in such a way that they are stimulated from without the body. 
The sense organs are the eye, the ear, the nose, the epithelium 
of the tongue and mouth, and the skin. The nerves in the 
eye are stimulated by light; the nerves in the ear by sound 
waves in the air; the nerves of smell by odors; the nerves of 

245 


246 


HUMAN PHYSIOLOGY 


taste by substances dissolved in the mouth; and the nerves 
in the skin by touching objects, and by heat and cold. The 
impulses that are thus started in these nerves travel up to 
the brain and cause sensations of light, sound, smell, taste, 
and touch. Seeing , hearing , smelling , tasting , and feeling are 
the five special senses, and by these senses we learn all that 
we know of the world about us. 


TOUCH 

Afferent Nerve Endings in the Skin. The upper surface 
of the dermis is thrown into papillae that stand up like little 



FIG. 113. Afferent nerve endings. A shows a nerve fiber in the skin ending at 
the bases of tactile cells. B shows a nerve fiber with free endings among the cells of 
the skin. The nerves of glands and of involuntary muscles, and the afferent nerves 
of voluntary muscles, end in this way. C shows a nerve fiber ending in a bulb of 
connective tissue. Many nerve endings of this kind are found in the lower layers of 
the skin, and in the internal parts of the body. 


mountain peaks under the epidermis. Some papillae of the 
skin (Fig. 93) contain only blood vessels, but in other papillae 















THE SPECIAL SENSES 


247 


tactile corpuscles (Fig. 94) are found. These are small, oval 
bodies, in which one or several nerves of touch end. The 
tactile corpuscles are especially abundant in the fingers and 
toes. 

Other nerves of touch branch at the ends, and have on the 
tip of the branch a little saucer-like expansion that fits 
around the base of an epidermal cell. Such a cell is called a 
tactile cell. Still others of the afferent nerve fibers of the 
skin end in many small free branches among the epidermal 
cells. 

How we feel. When we touch anything, the epidermis is 
pressed down on the ends of the nerves of touch. This 
starts an impulse up the nerve to the 
brain, and causes a sensation of feeling. 
If all the nerve endings in the skin that 
is being touched have the same amount 
of pressure on them, we know that we 
are feeling a smooth surface. If some 
of them are being pressed harder than 
others, we know that the surface is 
rough. We know what part of the body 
it is that is touching an object because we know which 
nerves are bringing the impulses. We know whether the 
object is large or small by the amount of skin that is touching 
it, and by the distance that we must move the hands to pass 
them over it. The mind is thus able to judge of many things 
by the nerve impulses that come to it through the nerves of 
touch. That it may form mistaken judgments from these 
impulses, you can prove by crossing your fingers (Fig. 114) 
and rubbing the point of your nose so that it will touch the 
outer edge of one finger and the inner edge of another finger. 
It will seem as though you had two noses, because ordinarily 



248 


HUMAN PHYSIOLOGY 


it takes two objects to touch the fingers on their edges as the 
nose is touching them, and the mind has come to think that 
there are two objects when impulses come from these points 
at the same time. 

Different Kinds of Afferent Nerves in the Skin. In the skin 
are nerves that are stimulated by touch, others that are stim¬ 
ulated by heat, and others that are stimulated by cold. 
Whether there are special nerves of pain, or whether any 
afferent nerve fiber, if stimulated in the wrong way, will 
cause pain, is not known. When the epidermis is removed, 
as by a burn, all sensations of touch, heat, and cold are lost, 
and only sensations of pain come from the part. That the 
nerves in the skin do not all do the same kind of work you 
can easily prove by the following experiment: 

Fill a small test tube with warm water, or warm the end of a wire 
or other piece of metal, and pass it slowly over the skin of the fore¬ 
arm. In certain spots you will feel a sensation of warmth. Mark 
these places by small drops of ink, and then pass a cold object over 
the same area of skin. Note that the nerves for feeling cold are not 
in the same place as the heat nerves. Also note that nerves of touch 
are found where there are neither heat nor cold nerves. 


Where the Sense of Feeling is Best In some parts of the 
skin the nerve endings are very abundant, and in these 
places the sense of touch is acute. In the 
tip of the tongue it is most acute of all. It 
is also very highly developed in the lips, in 
the tip of the nose, and in the finger tips. 
Thrust two pins through a thin piece of 
cork (Fig. 115) and touch them to the fin¬ 
ger tip. Here you can feel the two points 
when they are only one twelfth of an inch 
apart. But if you touch them to the back 
of the hand or forearm, they will feel like one point unless you 



Fig. 115. 



THE SPECIAL SENSES 


249 


place them much farther apart. On the tip of the tongue we 
can distinguish two objects that are only one twenty-fifth of 
an inch apart, while on the back of the body two objects must 
be separated by two and one half inches before we can tell 
whether one or two points are touching us. The following 
is an interesting experiment: 

Thrust two pins through a piece of cork, and while some member 
of the class is blindfolded, or looking the other way, touch his skin on 
the finger tips, back of the hand, forearm, lips, cheek, neck, etc. 
Sometimes use one pin and sometimes two, and measure how far 
apart the two must be separated before they can be distinguished on 
the different parts of the body. 


TASTE 

The nerves of touch are all over the body, but the nerves 
of taste end only in the tongue and in the epithelium 1 of the 
back part of the mouth. The taste nerves branch out and 
end free among the epithelial cells, and in some places in the 
tongue they end in a special way in little 
bodies that are called taste buds. A taste 
bud is composed of an outer circle of long 
cells, set edge to edge, as the staves are 
arranged in a barrel. It is buried in the 
epithelium of the tongue, and at the tip of 
the bud is a small opening out into the 
mouth. Within the bud are long, slender fig. 116. a taste bud 
taste cells , the tips of which stand up out 
of the opening in the end of the bud. Within the taste bud 
the nerves of taste are connected with the taste cells. 

Before anything can be tasted, it must first be dissolved. 
Then the little molecules of the substance work down in 

1 The outer layer of cells in a mucous membrane is called the epithelium . 
It corresponds to the epidermis of the skin. 





250 


HUMAN PHYSIOLOGY 


among the taste cells and so affect them that they start im¬ 
pulses in the nerve fibers behind them. These impulses go 
to the brain and cause sensations of taste. 

SMELL 

The olfactory nerves , or nerves of smell, end in the lining of 
the upper front part of the nasal cavities. In the mucous 
membrane of these parts are long, 
slender cells called olfactory cells. 
They lie between the epithelial 
cells, and their outer ends are di¬ 
vided into fine cilia-like processes. 
From the inner end of the olfactory 
cells nerve fibers pass to the brain. 
The olfactory cells are in reality 
fig. i 17. The olfactory nerves, nerve cells that have grown down 
from the brain above, and they are the only 
nerve cells in the body that are exposed to 
the outside world. 

How we smell. From anything that has 
an odor, molecules are flying off into the 
air. These molecules pass into the nasal 
chamber, come into contact with the olfac¬ 
tory cells, and there cause changes that 
start impulses up the olfactory nerves. 

Drawing the air up into the nose brings 
the molecules up to the olfactory cells, and 
we therefore sniff the air when we wish to 
smell anything. 

In certain animals the sense of smell is 
much more highly developed than it is 
in man. Some kinds of dogs can follow 



TO BRAIN 

FIG. 118. A por¬ 
tion of the olfactory 
mucous membrane. 
The slender cells with 
the cilia-like processes 
on them are the olfac¬ 
tory cells. 














The special senses 


251 


the track of an animal or man many hours after the trail has 
been made, and bees and some other insects are also far 
more keen-scented than is man. 

Care of the Olfactory Organ. Inflammation destroys the 
delicate olfactory cells, and when they have been destroyed 
they are not renewed. Inhaling dust is a common cause of 
inflammation of the mucous membrane of the nose, and taking 
cigarette smoke into the nose is very injurious to the olfactory 
cells. Catarrh should have medical treatment, for by it the 
sense of smell is partially destroyed in many persons, and it 
may lead to more serious diseases. 

HEARING 

Hearing is caused by waves of air striking against the ear. 
In order to understand this subject, it is necessary to under¬ 
stand something of the nature of air. In solid bodies, the 
molecules cannot move about from one place to another. In 
liquids, the molecules move about and slip over each other, 
but they do not separate. In gases, the molecules are not 
held together, but separate and fly off from each other. 

The air is a mixture of gases (page 178), and if the air 
molecules were visible, you would see the molecules of the 
different gases dancing and flying about and striking against 
each other. When the wind blows, the molecules are flying 
along. When the wind pushes against you, the many little 
molecules of which the air is composed are flying against you 
and striking you. In a great gale the air may be traveling 
at the rate of a mile a minute, and in very great storms it 
may even have a speed of two miles a minute. With a 
speed like this, its molecules strike objects in their path with 
tremendous force, uprooting trees, carrying away houses, and 
overturning large and heavy objects. 


252 


HUMAN PHYSIOLOGY 


Sound Waves. When you throw a stone into water, the 
stone strikes against the molecules of water and sets them in 
motion. The molecules which are set in motion by the stone 
strike against those next to them; these in turn hit the next 
set, and a wave runs out in the water. When a bell is rung, 
the bell vibrates and strikes the air molecules next to it, set¬ 
ting them in motion. These strike the next molecules, and 
so on, and a wave runs out through the air. When these air 
waves strike the ear, they start impulses in the auditory nerve, 
the impulses are carried to the brain, and we hear the bell ring. 
Big air waves cause loud sounds, and small waves cause slight 
sounds. Great sound waves may strike the ear with such force 
as to break the tympanic membrane (Fig. 119), and they may 
also break windows and jar houses. 

The Ear. The ear is an organ so constructed that when 
the sound waves strike it, the afferent nerves in it will be 

stimulated. It is divided into 
three parts, — the external 
middle, and internal ear. 

The External Ear. The ex¬ 
ternal ear includes the part 
that we see and the canal 
(auditory canal ) leading down 
to the middle ear. The ex¬ 
ternal ear is composed of a 
piece of cartilage covered 
with skin. Its function is to 
catch the sound waves and 
turn them down the canal to 
the middle ear. When animals are listening intently, they 
hold up their ears to catch as much of the sound waves as 
possible, and a man sometimes holds his hand behind his 



Fig. 119. The ear. 





THE SPECIAL SEHSES 


253 


ear to help in turning the sound waves down the canal to the 
middle ear. 

The Middle Ear. The middle ear is a little cavity in the 
temporal bone of the skull. The cavity is shaped like a 
drum, and is often called the tympanum , or ear drum. At 
the inner end of the auditory canal is the tympanic mem¬ 
brane. This stretches like a piece of thin skin across the 
bottom of the canal, and separates the external ear from the 
tympanum. The cavity of the tympanum is filled with air. 

The Bones of the Ear. In the middle ear are three very 
small bones, — the malleus (hammer), the incus (anvil), and 
the stapes (stirrup). The malleus 



is fastened to the tympanic mem¬ 
brane, the stapes fits into an open* 
mg that leads into the internal ear, 
and the incus is between the mal¬ 
leus and the stapes. These three 
bones stretch across the middle 
ear from the tympanic membrane 
to the inner wall. 


The Eustachian Tube. The 

Eustachian tube is a narrow pas¬ 
sageway that leads from the mid¬ 
dle ear to the pharynx. It enters 


Fig. 120. Bones of the ear. 


the pharynx high up in the side 

wall, opening almost into the back part of the nasal cham¬ 
ber. Through the Eustachian tube the air passes out of 
and into the middle ear, and keeps the pressure of the air 
within the tympanum the same as the outside air pressure. 
If a Eustachian tube becomes closed, 1 the varying pressure 

1 In colds, catarrh, scarlet fever, measles, pneumonia, and in some other dis¬ 
eases, inflammation may extend up the Eustachian tubes and cause deafness 





254 


HUMAN PHYSIOLOGY 


of the atmosphere caused by changing conditions of the 
weather and by passing to the lighter atmospheres of higher 
altitudes or the heavier atmospheres of lower altitudes, 
causes an unequal pressure on the two sides of the tympanic 
membrane. This causes deafness. 

The Internal Ear. The internal ear lies deep in the tem¬ 
poral bone, and is divided into three parts. The central 

part is the vestibule; the front 
part, which is coiled like a snail 
shell, is the cochlea; and the 
back part is the semicircular 
canals. The entire internal ear 
is filled with fluid. Standing 
out in this fluid from the 
walls are slender, hair-like cells, 
that at their inner ends are 
connected with the fibers of 
the auditory nerve. The im¬ 
pulses that cause us to hear 
come from the cochlea. 

How a Sound is heard. The external ear catches the sound 
wave and turns it down the auditory canal, at the bot¬ 
tom of which the wave strikes the tympanic membrane. 
The membrane swings out and in, and sets the chain of 
bones in motion. The malleus pushes on the incus, and the 
incus on the stapes. The stapes is thus forced in against the 
fluid in the vestibule and in this fluid waves are set up which 
run through the internal ear, striking against and moving the 
hair-like cells that project into the fluid. This starts im- 

by closing the tubes (page 270). Adenoid growths often close the Eustachian 
tubes and start inflammation in them. Probably two thirds of all deafness and 
ear trouble comes from this cause. 



Fig. 121. The internal ear. B shows 
the natural size of the internal ear. 



THE SPECIAL SENSES 255 

pulses that travel up the auditory nerve to the brain, and 
causes a sensation of sound. 

Function of the Semicircular Canals. The semicircular 
canals are not concerned in hearing, but their function is to 
assist in retaining the equilibrium of the body. One canal 
lies behind the vestibule in a vertical plane, and if the head 
moves forward or backward in the way that it moves in nod¬ 
ding, the fluid in this canal is set in motion. Another canal 
runs outward from the vestibule in a horizontal plane; when 
the head is turned to the side, as when one turns the head to 
look over the shoulder, the fluid in this canal is set in motion. 
The other canal runs up and outward from the vestibule in 
a vertical plane, so that if the head moves toward the side in 
the way it does when it is bent over toward the shoulder, the 
fluid in this canal moves. 

If the body leans in any direction, the fluid in one or more 
of these canals is always set in motion, and impulses are sent 
to the brain, bringing information in regard to the direction in 
which the body is beginning to fall. Impulses are then sent 
out from the brain that cause the proper muscles to contract 
and bring the body again to the upright position. Sometimes 
the semicircular canals become diseased, and then there is 
great difficulty in retaining the equilibrium of the body, be¬ 
cause it is not noticed that the body is beginning to fall. 
Sight and impulses from the muscles assist in keeping the 
equilibrium, but a prominent part of this work is done by the 
semicircular canals. 

Care of the Ears. A blow on the side of the head is danger¬ 
ous, for it may send such a strong air wave down the auditory 
canal that the tympanic membrane will be ruptured. Live 
insects in the ear may cause great distress by buzzing and 
moving about. They can be drowned by pouring oil or water 


256 


HUMAN PHYSIOLOGY 


into the ear. No one but a physician should attempt to re¬ 
move these or other objects from the ear, 1 because in doing so 
there is great danger that an unskilled person will injure the 
lining of the auditory canal or break the tympanic membrane. 

The hearing may be injured by quinine, and this should be 
taken for any considerable time only under the advice of a 
physician. Earaches and deafness are caused by various 
troubles, very often by catarrh that has spread up the Eusta¬ 
chian tube and affected the middle ear. Earache may some¬ 
times be prevented at night by wearing a hood or nightcap 
while sleeping, but wearing cotton in the ears and pouring 
oil and other liquids into them often brings on serious trouble, 
and should not be practiced. Children should not be left to 
outgrow ear troubles or they will often suffer great pain need¬ 
lessly, and perhaps will have the hearing permanently im¬ 
paired. Among adults about one third have the hearing 
affected in one or both ears largely because of neglect in 
youth. 

Summary. Some of the afferent nerve impulses cause sen¬ 
sation. General sensations are produced by impulses that 
arise within the body. In the special sense organs the 
nerves end in such a way that they are stimulated from out¬ 
side the body. Seeing, hearing, smelling, tasting, and feel¬ 
ing are the special senses. 

The afferent nerves of the skin end in tactile corpuscles, at 
the bases of tactile cells, and in free nerve endings. In feel¬ 
ing objects, stimuli are started in the nerves by pressure ; 
and from these stimuli the brain forms many judgments in 

1 The bitter wax in the auditory canal is secreted by small glands in the skin. 
It is a protection against insects. Scraping the wax out of the ears with the head 
of a pin or other piece of metal may cause the lining of the auditory canal to be¬ 
come inflamed, and greatly increase the quantity of wax secreted. 


THE SPECIAL SENSES 


25 7 


regard to the things that we touch. In the skin are nerves 
of touch, heat, and cold, and possibly nerves of pain. The 
sense of touch is acute in the tip of the tongue, lips, and fin¬ 
ger tips, and much less acute in some other parts of the body. 

Many of the fibers of the nerves of taste end free in the 
mucous membrane of the tongue and of the back part of the 
mouth. Other fibers end in taste buds. Before anything 
can be tasted it must be dissolved. 

The olfactory cells are nerve cells in the nasal mucous 
membrane. Impulses are started in these cells by odors. 
The olfactory cells are delicate nerve cells, and if they are 
destroyed, the sense of smell is permanently lost. 

A sound wave is produced by setting in motion the mole¬ 
cules of the air. When these waves strike the ear, they 
cause us to hear. 

The ear is composed of the external, internal, and middle 
ear. The external and middle ears are separated by the 
tympanic membrane. The middle ear contains the malleus, 
incus, and stapes. The Eustachian tube puts the air in the 
middle ear into communication with the outside air. The 
internal ear is composed of the vestibule, cochlea, and semi¬ 
circular canals. The canals assist in preserving the equilib¬ 
rium of the body. 

When a sound wave strikes the external ear, it is turned 
down the auditory canal and sets in motion the tympanic 
membrane. This moves the chain of bones in the middle 
ear, and they set up waves in the fluid in the internal ear. 
These waves start impulses in the nerves of hearing that 
are carried to the brain, and cause sensations of sound. The 
ear should have intelligent care, for many cases of defective 
hearing come from neglecting ear troubles in children. 


258 


HUMAN PHYSIOLOGY 


QUESTIONS 

What causes sensations? Name some of the general sensations. 
Where do the nerve impulses that cause these sensations originate? 
Name the special sense organs. How are the nerve endings in e-ach 
one stimulated? 

Give three ways in which the afferent nerves end in the skin 
How are impulses started in these nerves when we touch an object? 
Explain how we are able to judge of certain properties of objects by 
touching them. What different kinds of nerves end in the skin? 
Where is the sense of feeling acute? Where is it least acute? 

Give two ways in which the nerves of taste end in the tongue. 
Describe a taste bud. How is the nerve of taste stimulated? Does 
a chicken taste corn when it eats it? 

Where is the organ of smell located? Describe the olfactory cells. 
What kind of cells are they? What is an odor? How are impulses 
started in the olfactory cells? In what ways may these cells be injured ? 

Of what is air composed? Explain how a bell starts w r aves in the 
air. How do these waves cause the sensation of sound ? 

Name the three divisions of the ear. What is the function of the 
external ear? What is the middle ear called? Why? What and 
where is the tympanic membrane? Name the bones of the ear. 
Where are the Eustachian tubes? What is their use? 

Name the parts of the internal ear. With what is it filled? Ex¬ 
plain how a stimulus is started in the auditory nerve. What is the 
function of the semicircular canals ? How are the impulses started 
in the nerves that are connected with these canals? When one whirls 
himself rapidly about and then stops, what causes him to have a sen¬ 
sation of dizziness? 

How may a blow on the ear injure the hearing? How may an 
insect in the ear be killed ? What is a common cause of earache and 
deafness? Why should ear troubles in children receive attention? 


CHAPTER XX 


THE SPECIAL SENSES (Continued): SEEING 

All space is filled with an invisible substance called ether , 
and light is waves in the ether. The eye is so constructed 
that when the ether waves enter it, they stimulate the affer¬ 
ent nerves and start impulses to the brain that cause the 
sensation of sight. 

Protection of the Eyes. The eyes are very important and 
very delicate organs, and must therefore be well protected. 
The deep bony eyesockets are a great protection from blows. 
The inside of the eyesocket is lined with a layer of fat which 
forms a soft cushion for the eyes to rest and turn on, and if 
the eye is struck, the fatty layer between it and the bone 
assists in preventing injury. 

The eyelids, eyelashes, and eyebrows also assist in protect¬ 
ing the eyes. The eyelids screen them from dust and light, 
and close if a blow is threatened. The eyelashes guard the 
eyes from dust and light, and the eyebrows keep the sweat 
from running down from the forehead into the eyes. 

The Lachrymal Glands. In the outer corner of each upper 
eyelid is located a lachrymal gland, very similar in structure to 
a small salivary gland. These glands secrete the tears and 
pour them into the eyes at the upper outer corners. The tears 
flow down across the eye to the inner corner, where they enter 
the lachrymal duct , which carries them down into the nasal 
chamber. In their passage across the eyes, the tears cleanse 

259 


26 o 


HUMAN PHYSIOLOGY 


the eye, washing away dust and germs. The workings of the 
lachrymal glands give us another illustration of the effect of 

the mind on the body; for 
sorrow, pain, and sometimes 
anger cause them to secrete so 
abundantly that the tears cannot 
all be carried away by the lach¬ 
rymal ducts, but overflow on the 
cheeks. 

The Meibomian Glands. In 

i-ig. 122. The lachrymal gland and th e eyelids are small glands 

called the Meibomian glands. 
They are very similar to sebaceous glands, and empty out 
an oily secretion along the edges of the eyelids. Water 
does not flow freely over an oiled surface, and the secretion 
from the Meibomian glands prevents the tears from over¬ 
flowing the eyelids. When the 
eyelids are inflamed and con¬ 
gested, the Meibomian glands 
sometimes become diseased, 
and the secretion from them 
dries around the roots of the 
eyelashes, forming scales very 
similar to dandruff. 

The Muscles of the Eyes. 

There are six muscles to move 
each eye. The back ends of 
these muscles are attached to the walls of the eyesocket. The 
front ends are attached to the ball of the eye. By these 
muscles, the eyes can be turned in any direction, so that it is 
not always necessary to turn the head toward the object at 
which we are looking. 



Fig. 123. The muscles of the eye. 






SEEING 


261 

The Structure of the Eye. The eye has three coats. The 
outer one is the sclerotic coat, the middle one is the choroid 
coat, and in the back part of the eye is a third inner coat 
called the retina. The optic nerve enters the eye at the back 
and spreads out in the retina. 



The interior of the eye is divided by the lens and the 
ligaments that support the lens into a small anterior cham¬ 
ber and a larger posterior chamber. The posterior chamber 
is filled with a transparent, jelly-like substance, called the 
vitreous humor. The small anterior chamber is filled with 
the aqueous humor , a watery fluid similar to tears. 

The Sclerotic Coat. The sclerotic coat, or white of the 
eye, is composed of dense, closely woven connective tissue. 
It has a white color, except in front, where it is transparent. 
This transparent part is called the cornea i and through it the 




262 


HUMAN PHYSIOLOGY 


light passes into the interior of the eye, as light passes 
through a window into a house. 

The Choroid Coat and the Iris. The choroid coat is a loose 
connective tissue coat. It contains pigment that gives it a 
rich, dark color similar to the inside of a grape skin. The 
front part of the choroid is called the iris. This contains a 
circular opening, the pupil , in its center. The iris lies behind 
the transparent cornea, and being seen through the cornea, 
gives the color to the eye. A person is black-eyed, brown¬ 
eyed, or blue-eyed, according to the pigment in his iris. 

The Function of the Iris. The function of the iris is to 
regulate the amount of light that enters the eye. In the iris 

are circular muscle fibers, run¬ 
ning around the pupil, and 
when these contract, they 
make the pupil smaller. 
Other muscle fibers run in 
from the outer edge of the 
iris to the pupil, and when 
these contract, they enlarge 
the pupil. 

The control of the size of the pupil is carried on by invol¬ 
untary reflexes. When a strong light enters the eye, the 
circular fibers in the iris contract and diminish the size of the 
pupil. When the light is weak, the pupil is enlarged and 
more light is admitted to the eye. When you step out of a 
brightly lighted room into the dark, you cannot see, because 
the pupil is too small to allow enough light to enter. But if 
you remain out in the dark, the pupil will be enlarged and 
admit more light, and your vision will become better. When 
you step from a darkened room out into the bright sunshine, 
the light dazzles the eyes, because the opening in the pupil 



Fig. 125. One cat has been in the dark; 
the other has been in the light. 


SEEING 


263 


is too wide and lets in too much light. After a few minutes, 
the muscles of the iris contract and diminish the size of the 
pupil, thus adapting the eye to the bright light. 

The eye of a cat shows very distinctly the changes in the 
size of the pupil. In the dark the pupil is large and round, 
and in a bright light it is narrowed to a slit. This you can 
easily see for yourself by examining the eye of a cat that has 
been in the light, and then shutting the cat in a dark room 
or closet and examining its eye again. 

Owls have very large pupils, which enable them to see at 
night better than most animals and birds; but in a bright 
light the pupil of an owl’s eye cannot be made small enough 
to keep the eye from being dazzled by the light. Many 
animals (the cat and the horse are examples) can see at night 
better than man can see, because the pupils can be opened 
wider than can the pupil of the human eye. 

The Lens. The lens (Fig. 129) lies close against the back 
of the iris. It is thin at the edges and thicker in the 
middle, and is composed of a clear, jelly-like substance. 
The lens is inclosed in a circular sac, and both the sac 
and the material in it are transparent, so that the light 
can pass through them to the retina in the back of the 
eye. The lens is attached to the choroid coat by the suspen¬ 
sory ligament , which runs out all around from the outer edge 
of the lens. Figure 124 shows the lens and the suspensory 
ligament as they appear when cut across, but you must 
understand that the lens is circular like a coin, and that the 
suspensory ligament is a ring with the lens fitted into the 
opening of the ring. 

The Function of the Lens. The function of the lens is to 
form images of the objects that we see , and to accommodate the 
eye to near and distant objects . In forming images in the 


264 


HUMAN PHYSIOLOGY 


eye, the lens is assisted by the curved surface of the cornea. 
On the ground glass in the back of a camera, you can see 
an image formed by the lens in the front of the camera. 
The lens and cornea of the eye form images on the retina 
in the same way that the image on the camera is formed. 

How a Lens forms an Image. Hold a convex lens 1 so that 
sunlight will pass through it. You 'will find that the lens 
brings the rays of light to a focus, — that is, it bends them so 
that they all meet in one point. It does this by changing the 



directions in which the light waves are running, causing 
them all to run toward one point. The lens of the eye 
bends all the rays of light that come from one point , so that 
they meet in one point on the retina of the eye. In Figure 126 
you can see how all the rays of light from the point of the 
arrow meet in one place and form an image of the arrow 
point. In the same way, an image of the other end of the 
arrow is formed, and of every other point in the arrow , and 
all these points together make an image of the arrow. So, 
in looking at a landscape, an image of the whole landscape 
is formed in the eye, all the rays of light that come from any 
one part of the scene in front of the eye meeting in one point 
and forming an image of that point on the retina. The 

1 This experiment can be performed with the lens in a pair of convex 
spectacles. 








SEEING 


265 


images that are formed in the eye, like the images in a 
camera, are upside down, and the right 
and left sides are reversed. 

The Retina. The retina contains slen¬ 
der, pointed cells that are affected by 
light. These cells are connected with 
the optic nerve, and when light strikes 
the retina an impulse is started which 
passes back through the optic nerve to 
the brain. 

The Function of the Brain in seeing. 

Impulses are started in the eye by the 
images that fall on the retina, but these 
impulses must be carried to the brain be¬ 
fore the sensation of sight is produced. 

From the impulses that come into the 
brain from the eye, we form judgments 
in regard to the form, size, color, and 
smoothness or roughness of objects. 

0 J Fig. 127. When light 

From these impulses we can judge also strikes the retina, impulses 
of the distance of objects from US, of are started in the long, slen- 
their relative positions, and of their retina . T ' hese are ' carried 
movements. That the mind does not to the brain, and cause the 
always form correct judgments from sensation of sight, 
the impulses that come from the eye, you can easily dem¬ 
onstrate by looking at the two lines 
of the same length in Figure 128. 

The Accommodation of the Eye. 
The shape of the lens must be 
changed according to the distance 
from the eye of the object that we 
fig. 128. are looking at. When the object is 

























266 


HUMAN- PHYSIOLOGY 


close to the eye, the lens must be 
made more convex; for a distant 
object the lens needs to be flat¬ 
tened. This change in shape of 
the lens is called the accommoda¬ 
tion of the eye and is brought 
about by the ciliary muscles. 

How the Eye is accommodated. 
The suspensory ligament is at¬ 
tached to the choroid coat as is 
shown in Figure 129. The front 
ends of the ciliary muscles are 
attached to the sclerotic coat. 
Their other ends are attached to 
the choroid coat. When these 
muscles contract, they stretch the 
choroid and draw it forward. 
This loosens the suspensory liga¬ 
ment, and the lens of itself rounds 
Fig. 129. when the ciliary mus- out and becomes more convex. 

des contract they draw forward the when the ciliary muscles relax, 
choroid coat, loosen the suspensory , , , . , 

ligament, and allow the lens to be- the stretched choroid returns to its 
come more convex. former position, thus tightening 

the ligament again and flattening the lens. 

The change in shape of the lens can be illustrated with a 
small sac, or with the swimming bladder of a fish, filled with 
air or water. Pull on the ends of the sac, and you will flatten 
it. Decrease the pull, and of itself the sac will round up, as 
does the lens when the ligament is loosened by the choroid’s 
coming forward. You should take especial care to note 
that the contraction of the ciliary muscles loosens the 
ligament, and does not tighten it, for pupils who are 








SEEING 267 

studying the eye often get an incorrect idea in regard to this 
point. 

Near-sightedness. The image in the eye must fall exactly on 
the retina, or vision cannot be distinct. In some persons, the 
eyes are long from the front 
to the back. In such persons, 
the rays of light meet before 
they reach the retina. This 
makes an indistinct image, as 
does a camera, microscope, or 
field glass, when it is out of 
focus. In B (Fig. 130) you can 
see how the rays of light from 
the head of the arrow meet in 
front of the retina, and how, 
when they reach the retina, 
they have crossed and sepa¬ 
rated again, scattering the 
image on the retina instead of 
making it clear and distinct at 
one point. In such an eye, 
the images of the different 
points overlap, and a blurred, 
indistinct image of the whole object is the result. Near¬ 
sighted persons usually have prominent eyes, and the cornea 
usually is more convex than it is in the normal eye. 

Far-sightedness. A far-sighted eye is too short from front 
to back. In such an eye, the retina is so close to the lens 
that the rays of light have not been brought together when 
they get to it, and the image is blurred (Fig. 130 C). Per¬ 
sons with eyes of this kind see distant objects best, because 
the rays from these objects meet more quickly than do those 



FIG. 130. A, normal; B, near-sighted; 
and C t far-sighted eye. 










268 


HUMAN PHYSIOLOGY 


from near objects. In a far-sighted eye, the cornea is usually 
flatter than it is in the normal eye, and in far-sighted per¬ 
sons the eyes are not so prominent as they are in near-sighted 
persons. 

Astigmatism. In astigmatism, the curvature of the cornea 
is uneven, some parts being flatter than other parts. The 
rays of light that pass through the flatter places on the 
cornea are not brought to a focus as soon as the rays passing 
through the more convex parts. A distinct image cannot be 
formed in such an eye, for the lens cannot be so shaped that 
all the rays from one point will come together in a single 
point on the retina. 

Eyes of Old Persons. In old persons, the material of which 
the lens is composed becomes harder and less fluid, and when 
the suspensory ligament is slackened, the lens fails to change 
its shape. The power of accommodation is thus lost. One 
of the most wonderful things about the eye is the way it 
accommodates itself to objects at different distances, and in 
old persons this power is to a certain extent lost. 

Spectacles. If a sharp, clear image is not formed on the 
retina, eye trouble is certain to result. Near-sighted, far¬ 
sighted, and astigmatic eyes need spectacles or eyeglasses 
to assist in forming distinct images on the retina. The kind 
of lenses that are needed in the spectacles depends on where 
the image falls in the eye, each particular eye needing to be 
fitted with a lens that will cause the image to fall exactly on 
the retina. 

Concave lenses spread the rays of light farther apart. If a 
concave lens is placed before a near-sighted eye, the lens will 
spread the rays of light and cause them to meet farther back 
in the eye (Fig. 131). A person who is very near-sighted 
will need a strongly concave lens, and a person who is only 


SEEING 


269 


a little near-sighted will need 
only a slightly concave lens. 
Each eye needs a lens that 
will bring the rays to a focus 
on the retina. 

Convex lenses bend the rays 
of light together and cause 
them to meet more quickly. 
In far-sighted eyes, the rays 
have not yet met when they 
reach the retina, and by plac¬ 
ing a convex lens before such 
an eye, the rays can be 




Fig. 131. How glasses cause the rays 
of light to meet on the retina. 


brought together and made to meet on the retina. 

In astigmatic eyes, the lens must be ground to suit the eye. 
Where there is a little hill on the cornea, a concave place 
must be ground out in the lens, and where there is a flat 
place on the cornea, the lens must be convex. Old persons 
need one pair of glasses for seeing distant objects, and another 
pair for seeing near objects. 


HYGIENE OF THE EYES 

It is a great mistake to think of the eye as a separate part 
of the body, doing its work without connection with the other 
body parts. Like all the other organs, it is intimately related 
to the rest of the body, and any defect or trouble in the eye 
is likely to affect other organs, the nervous system, and the 
general health. It is, therefore, important to care for the eyes, 
not only to relieve pain in the eyes themselves and to have 
good vision, but for the purpose of keeping the entire body in 
health. 













270 


HUMAN- PHYSIOLOGY 


Care of the Eyes. Spectacles or eyeglasses should be worn 
when they are needed. In securing these, one should always 
go to a reliable physician or oculist, and not to some unskilled 
person or traveling optician, for it requires considerable skill 
and care to examine an eye, and to tell exactly the kind of 
lens that is suited to it. Also, the eye sometimes changes 
very rapidly, so that the lenses of the spectacles need to be 
changed, and it is always better to deal with some one who 
can examine the eyes from time to time, and change the 
lenses as changes are needed. 

The importance of having the eyes properly fitted with 
glasses cannot be too strongly insisted on, for many cases of 
nervousness, headache, indigestion, nausea, and mental dull¬ 
ness vanish as if by magic when glasses are adjusted to the 
eyes. 1 If a person has any signs of eye trouble, or if he has 
headaches and stomach trouble for which there seems to be 
no reason, the eyes should be examined at once. 

A good light should always be used in reading or in doing 
other close work. To read by a dim light, as when one reads 
on into the twilight, is exceedingly injurious. A dazzling, 
bright light is also injurious, especially if it shines directly 
into the eye. In reading, one should sit so that the light will 

1 To the Teacher : A considerable proportion of the children who are re¬ 
garded as dull in school fall behind their classes because of defective hearing or 
vision. The teacher should carefully watch his dull pupils for symptoms of 
trouble in the nasal passages, test the hearing by some such device as trying how 
far the child can hear the ticking of a watch, and note if the child holds his 
book close to his eyes or shows other symptoms of eye trouble. The attention 
of parents should be called to any defects that may be discovered, and the parents 
should be made to understand the importance of medical attention for such 
cases. Any close work is injurious to the eyes of young children, and kinder¬ 
garten teachers especially should take care to see that the eyes of the children 
in their charge are not injured by too much sewing, weaving, or other similar 
worjc. (See also page 308, note 1.^ 


SEEING 


271 


fall on the book, but not into the eyes. Facing a window in 
the daytime is injurious,and it is also injurious to read on a 
dark day in a corner of a room far from a window. 

Reading while lying down is a bad practice y because in this 
position, too great a blood supply comes to the eyes, and they 
become congested with blood. Then, too, the book or paper 
is often held in a very awkward position, which strains the 
eyes. 

Resting the eyes occasionally is very helpful. In reading, 
the eye is accommodated for near objects, and the ciliary 
muscles must be held contracted to round up the lens. In 
reading for long periods of time, these muscles become ex¬ 
hausted. It is, therefore, a good idea to stop occasionally 
while reading, and to close the eyes or look out of a window 
at a distant object, allowing the ciliary muscles to relax and 
rest. This advice applies of course when one is doing any 
work that is hard on the eyes. 

Dust is exceedingly injurious to the eyes. It always causes 
irritation by scratching the surface of the eye and the lining 
of the eyelids, and it carries into the eye germs that may 
cause inflammation. For congestion and redness of the 
eyes, bathing in cold water is helpful. A little boracic acid 
dissolved in water (the exact strength of the solution is not 
important) and dropped into the eyes at night on retiring 
has a very soothing effect on the eyes, and helps to kill 
germs that get into them. But in any serious o.r long-con¬ 
tinued trouble with the eyes, a physician or oculist should 
always be consulted. 

Effect of Tobacco and Alcohol on the Eyes. In a few per¬ 
sons, tobacco affects the nerves of sight so that distinct vision 
and the power of distinguishing between colors are lost. 
Tobacco smoke is irritating to the eyes, and in a considerable 


2J2 


HUMAN PHYSIOLOGY 


number of persons, smoking brings on a congestion and red¬ 
ness of the eyes and eyelids. Alcohol congests the vessels 
of the eyes, as it does those of other parts of the body, but 
the effects of alcohol and tobacco on the eyes in most cases 
are not very serious, as compared with their effects on some 
of the other organs of the body. 

Summary. The eye is protected by the eyesocket, the eye¬ 
lids, eyelashes, and eyebrows. It is cleansed by tears that are 
secreted by the lachrymal gland and are drained off into the 
nose by the lachrymal duct. The edges of the eyelids are 
kept oiled by the Meibomian glands so that the tears will 
not overflow on the cheeks. 

The eye is moved by six muscles. It has three coats, — 
the sclerotic coat, choroid coat, and retina. Its interior is 
divided by the lens and the suspensory ligament into an ante¬ 
rior and a posterior chamber. The anterior chamber contains 
the aqueous humor; the posterior chamber contains the vitre¬ 
ous humor. 

The transparent front portion of the sclerotic coat is called 
the cornea, and the front portion of the choroid coat is the 
iris. The iris gives the color to the eye. In the center of 
the iris is an opening called the pupil. The muscles in the 
iris open and close the pupil and in this way regulate the 
amount of light that enters the eye. 

The lens and cornea form images on the retina of the eye. 
The images start impulses to the brain that give us the sensa¬ 
tion of sight. The eye is accommodated for near and far 
objects by changing the shape of the lens. 

It is essential to clear vision that the image fall on the 
retina. Eye troubles cause headaches and a derangement of 
the digestive and nervous systems. When spectacles are 
needed, they should be worn. A good light should be used 


SEEING 


273 


in reading, and occasionally the eyes should be rested. Dust 
is harmful to the eyes and tobacco and alcohol may in¬ 
juriously affect them. 

QUESTIONS 

What is light ? What does light do when it enters the eye ? 

How is the eye protected? Where are the lachrymal glands? 
the lachrymal ducts? the Meibomian glands? What is the function 
of the Meibomian glands? 

How many muscles move each eye? Where are these muscles 
attached? Name the coats of the eye; the two chambers of the 
eye. What separates the two chambers? Where is the vitreous 
humor? the aqueous humor? 

Of what is the sclerotic coat of the eye composed? What does 
the choroid coat contain? What is the cornea? iris? pupil? 
What is the function of the iris? How is the size of the pupil 
changed ? Under what conditions does it enlarge and contract ? 

Describe the lens. How is it held in place? What is its func¬ 
tion? Explain how an image is formed by a lens. Describe the 
cells in the retina and tell how nerve impulses from these cells 
reach the brain. What part has the brain in seeing? 

Where are the ciliary muscles attached ? Explain how the eye is 
accommodated. 

What is the trouble in a near-sighted eye? in a far-sighted eye? 
in an astigmatic eye ? in the eyes of old persons ? 

What effect have concave lenses on light waves that pass through 
them ? convex lenses ? What kind of lenses are needed in specta¬ 
cles for near-sighted eyes? for far-sighted eyes? for astigmatic 
eyes? 

What are some of the ailments brought on by eye trouble? Why 
is it important to wear spectacles when they are needed? From 
whom should they be procured? Mention three points that should 
be kept in mind in caring for the eyes. Why is dust injurious to 
the eyes? What effect has tobacco on the eyes? alcohol? 


CHAPTER XXI 

ACCIDENTS 


In cases of accidents and emergencies it is often very im¬ 
portant that something be done at once. Some of the best 
measures to be employed in such cases will be discussed in 
this chapter. When the time comes for putting these measures 
into use, a cool head and quick action are absolutely neces¬ 
sary. Therefore, at such times, keep cool, think quickly, and 
act sensibly and at once. 

How to keep Afloat in Water. It requires very little force 
to keep the human body afloat in water. In trying to keep 
afloat, therefore, keep your body low in the water . A small 
board is enough to keep you afloat if you will do this. If 
thrown into the water by the upsetting of a small boat, do 
not try to climb upon the boat, or you may sink it. Keep 
your body low in the water and support yourself by taking 
hold of the boat with your hand. If you break through the 
ice, keep your body low in the water 
and take hold of the edge of the ice 
with your hand. Every one should learn 
to swim, for knowing how to swim 
even a few yards will often save life. 
How to revive a Person who has 
fig. 132. Draining the been under Water. In drowning, the 

water from the lungs. trouble ^ ^ ^ ^ ^ ^ off frQm 

the lungs by the water. The great point, therefore, is to get 
air into the lungs as quickly as possible. 

274 



ACCIDENTS 


275 


The first thing is to drain the water from the lungs. Turn 
the patient on his face and lift him as is shown in Figure 132. 
Lift him up two or three times, jerking the body, so that all 
the water will come out of the lungs. Do this quickly (in 
about thirty seconds). 

After the water is out of the lungs, turn the patient on his 
back. Put something — a pillow, clothes, anything at hand 
— under the shoulders to throw the chest out. Loosen the 
clothing at the neck and waist. The tongue must be drawn 
out of the mouth and 
either held or fastened by 
having a pin thrust through 
the tip. Otherwise it will 
drop back and close the 
throat. All this must be 
do?ie quickly , for life often 
depends on starting respi¬ 
ration at once. 

The next step is to start 
artificial respiration. To 
do this, grasp the patient’s 
arms and pull them up far 
over his head (Fig. 133 A) 
while you count one, two, 
three. Then bring the 
arms down to the sides and 
press as hard as possible 
on the sides of the chest to force the air out of the lungs. 
Do this about twelve or fifteen times a minute. If the 
patient does not begin to breathe in three or four minutes, 
turn him over and try if any more water can be drained from 
the lungs. 





276 


HUMAN PHYSIOLOGY 


When there are two persons to care for the patient, they 
should take the positions shown in Figure 134, and when 

the arms are brought 
down to the sides, one 
should press on the 
abdomen and chest 
in such a way as to 
force in the ribs and 
drive the abdominal 
organs and diaphragm 
upward. Keep up 
artificial respiration 
for two hours, if 
necessary, for per- 

FIG. 134. Artificial respiration carried on by two persons. gong ^ave revived 

after showing no signs of life for this length of time. 

A newer and better method is shown in Figure 133 B. 
About fifteen times a minute the weight of the body is 
thrown forward on the hands and then the pressure is re¬ 
moved without lifting the hands. In this method the tongue 
requires no care, and more air passes through the lungs than 
passes through them when the patient is laid on his back. 

Other treatment is useful when there is help enough to give 
it without interfering with the artificial respiration. The limbs 
should be rubbed upward to make the blood in the veins flow 
to the heart, and, if possible, the wet clothing should be re¬ 
moved and the body wrapped in warm blankets. Often the 
easiest way of warming the patient is to pour warm water 
over his clothing and then cover him with a blanket. Hot- 
water bottles or other warm objects will help to keep up the 
heat. In cold weather the warming of the patient is a very 
important part of the treatment. After the patient begins to 






ACCIDENTS 


2 77 


breathe, he should be kept warm, the head being warmed as 
well as the body. Hot water or hot coffee is useful. A little 
alcohol or 15 drops of ammonia in one third of a glass of 
water every fifteen minutes is also helpful. 

Suffocation. In suffocation the trouble is lack of oxygen, 
and artificial respiration is the remedy. 

Bleeding. When a large artery is cut, the blood flows from 
it in spurts. When a vein is cut, the blood comes from it in a 
steady stream. Sometimes the bleeding can be stopped by 
pressing on the cut vessel with 
the fingers. If an artery has 
been cut, the pressure must be 
applied between the wound and 
the heart. If a vein has been 
cut, the pressure should be ap¬ 
plied on the side of the wound 
away from the heart. Can you 
explain why this is the case ? 

When the wound is in a limb, 
a handkerchief or other piece 
of cloth should be knotted and 
tightly twisted about the limb, 
as shown in Figure 135. The 
knot in the handkerchief should 
be placed over the cut blood 
vessel, and if this does not 
stop the bleeding, a small stone or a piece of wood should be 
slipped under the knot. The best place to close an artery in 
the leg is on the inside of the thigh, or behind the knee, 
because at these points the arteries can be pressed against 
the bones. The upper arm is the easiest place to cut the 
blood off from the arm. When the wound is in a part of the 



FIG. 135. Stopping bleeding from 
an artery in the leg. 



2 y 8 


HUMAN PHYSIOLOGY 



FIG. 136. Stopping bleeding 
from an artery in the arm. 


body around which something cannot be twisted, cloths should 
be folded and pressed down on the wound. Any part of the 
body from which blood is escaping 
should be raised, for the blood al¬ 
ways flows more easily to a part of 
the body that is lowered. 

Fainting. Fainting is caused by a 
lack of blood in the brain. In treat¬ 
ing a person who has fainted, it is 
most important to lay him flat and 
loosen all clothing about the neck so 
that the blood can readily flow to 
the head. Fresh air is beneficial, 
and sprinkling the face with cold 
water or causing the patient to smell 
ammonia salts may assist in bring¬ 
ing him back to consciousness. When fainting is followed by 
weakness, a few drops of ammonia in a little water (15 drops 
of ammonia in one third of a glass of water for an adult) 
will prove a helpful stimulant. 

Sunstroke. Lay the patient in the shade and pour cold 
water on or apply ice to the head, back of the neck, and 
spine. 

Foreign Bodies in the Eye. Foreign particles may be re¬ 
moved from the eye by turning back the eyelid over a match 
or similar object, and wiping off the foreign body. The eye 
should not be rubbed or the particle may become embedded 
in the lining of the eyelid or in the outer surface of the eye. 
Holding up the eyelid while the eye is moved about sometimes 
brings the particle down to where it can be removed. Some¬ 
times the offending body may be washed out by bathing 
the eye. 




ACCIDENTS 


279 


Burning Clothing. If your clothing should take fire, do 
not start to run . Lie down and wrap yourself in a rug, 
blanket, or anything you can lay hands on, to smother the 
flames. If no rug or blanket is at hand, lie down and roll 
over and over. In any case be sure and lie down to prevent 
the flames from coming up around your face, for inhaling a 
flame is often fatal. 

When the clothing of another person is on fire, wrap him 
in something to smother the flames, and throw him down. 
Protect your own face as much as possible while doing this. 
In a burning building hold something before your face when 
near a flame. 

Treatment of Burns. Moisten the clothing with water and 
clip it away from the wound. Do not tear the skin. Rather 
than do this, leave patches of clothing sticking to the wound. 
Blisters should not be broken, but the liquid in them should 
be drained off by making small holes with a needle in the 
sides of the blisters. The treatment for burns made with hot 
water is the same. 

Shut the air offfrom the burn. The following are conven¬ 
ient methods of doing this : 

Cover the wound with clean cotton cloths that have been 
dipped in olive (sweet) oil. If carbolic acid and glycerin are 
at hand, add a teaspoonful of each to a pint of the oil before 
it is used. 

Stir baking soda into vaseline and cover the wounds with 
cloths on which this has been spread. 

Soak cloths in water in which as much soda as possible 
has been dissolved, and spread them over the wound. 

When nothing else is at hand, cover the wound with white 
of egg, wet starch, or wet flour. Do not cover a burn with 
cotton, or the cotton will stick to the flesh and cause trouble. 


2 8o 


HUMAN PHYSIOLOGY 


Great care should be used to keep a burn from becoming 
infected with germs (page 312). Unless it does become in¬ 
fected, it is best not to open it for some time, but to keep the 
cloths with which it is covered moist with sweet oil in which 
there is a little carbolic acid and glycerin. 

Poisoning. When any poison except an acid has been 
swallowed, vomiting should be induced at once. To cause 
the vomiting, stir a tablespoonful of mustard in a glass of 
water, take half of it, drink a large quantity of hot water, 
and follow it with the remainder of the mustard. Large 
amounts of warm salt water or simply warm water may be 
used when no mustard is at hand. Tickling the throat with 
a feather or thrusting the finger down the throat will often 
bring on the vomiting. 

Acids. Give soda, chalk, old mortar, or soap in plenty of 
warm water, and then cause vomiting. Oil and milk are also 
useful. For carbolic acid alcohol, oil, or milk should be used. 

Arsenic. Cause vomiting and give hydrated sesquioxid of 
iron. This compound may be formed by adding tincture of 
iron to baking powder. Give some of the brown powder 
that is formed to the patient every few minutes. The poison 
in Paris green, Fowler’s solution, and Rough on Rats is 
arsenic, and the treatment for poisoning with them is the 
same as the treatment for poisoning with arsenic. 

Belladonna. This is the poison in nightshade. Use the 
treatment for it that is given below for opium. 

Mercuric Chlorid. (Also called bichlorid of mercury and 
corrosive sublimate.) Give milk and white of egg or both. 
Flour or starch with milk and eggs is also a good remedy. 

Phosphorus. Magnesia and chalk in water and the white 
of egg are good remedies. Do not give oil or milk. Phos¬ 
phorus is in the substance on the ends of matches, and phos- 


ACCIDENTS 


28l 


phorus poisoning usually comes from allowing children to 
play with matches. 

Opium . Give strong coffee or ammonia (15 drops in one 
third of a glass of water every fifteen minutes or oftener). 
Walk the patient about, slap him, throw cold water on him, 
and do not allow him to go to sleep. Morphine, laudanum, 
cholera mixtures, paregoric, and soothing syrups are all either 
forms of opium or contain it. 

Strychnin . Inhaling chloroform or ether will quiet the 
patient. Give five grains of sodium bromid every half hour. 
Ammonia (see under Opium) or camphor in water is useful. 
Throw cold water over the patient and use artificial respira¬ 
tion if necessary. 

Stramonium. This is the poisonous substance in Jimson 
weed. The treatment for poisoning with at is the same as 
the treatment for opium poisoning. 

It is to be remembered that in poisoning with any of the 
above substances except acids, one of the most important 
things is to cause vomiting promptly. In acid poisoning it 
is usually best to give something to destroy the acid (page 
280) before the vomiting is induced. 

Summary. In accidents and emergencies a cool head and 
prompt action are important. 

It is much easier for a person to keep afloat when his 
body is low in the water than when he tries to climb up 
out of the water. To revive a person who has been under 
water, the water should be drained from the lungs and artificial 
respiration started at once. This should be kept up for at 
least two hours. It is also important to keep the patient 
warm. 

Suffocation is due to lack of oxygen, and artificial respira¬ 
tion is the treatment for it. 


2 82 


HUMAN PHYSIOLOGY 


Bleeding from a large vessel may be stopped by pressing 
on and closing the vessel. Fainting persons should be laid 
flat so that the blood will flow to the head. In sunstroke 
the patient’s head and spine should be cooled. 

Running when the clothes are on fire fans the flames. In 
such an emergency one should lie down and smother the 
flames with a rug or blanket, or put them out by rolling over 
and over. In all cases of fire, care should be taken not to 
inhale the flame. In a burn the skin should not be torn, but 
the wound should be covered from the air. 

In poisoning, vomiting to get the poison out of the stomach 
is a very important part of the treatment. In acid poison¬ 
ing it is best to give something to destroy the acids before 
vomiting is caused. Other treatment should be given accord¬ 
ing to the poison. 


QUESTIONS 

In trying to keep afloat, where should the body be allowed to 
remain? What causes death in drowning? In attempting to re¬ 
vive an apparently drowned person, what is the important thing to 
do? 

What is the first thing to do in attempting to revive a person who 
has 5 been under water? How is this done? In what position should 
the patient then be laid? Why must care be exercised in regard to 
the tongue? Explain how artificial respiration may be carried on 
by one person ; by two persons. How long should it be continued if 
the patient does not sooner revive? Describe another method that 
one person may use in causing artificial respiration. What is the 
advantage of this method ? What other treatment should be given 
where possible? 

What causes death in suffocation ? What treatment should be 
given? 


ACCIDENTS 


283 


When a large artery is cut, how does the blood flow from it? 
How does the blood flow from a vein? Where should pressure be 
applied to close a cut artery? a vein? Explain how bleeding from 
a cut in a limb may be stopped. Where is the best place to apply 
pressure to shut off the blood from the leg? from the arm? How 
may bleeding from a cut in some other part of the body be stopped? 

What causes fainting? How should a fainting person be treated? 
What treatment should be given in sunstroke ? 

What should one not do if his clothing takes fire ? What are the 
best ways of extinguishing the flame ? Why is it important to pro¬ 
tect the face from flame? 

What two important points should be kept in mind in dressing a 
burn ? How may the air be kept from a burn ? 

What is an important part of the treatment in poisoning? 


284 


HUMAN PHYSIOLOGY 


REVIEW QUESTIONS 

Chapter XVI. How does the nervous system resemble a telephone 
system ? Give the functions of the cerebrum; of the cerebellum; 
of the pons; of the medulla; of the spinal cord. Explain how a 
reflex action is carried out. Define : ganglion ; neuron ; afferent; 
efferent; convolutions ; arbor vitae; acquired reflex. 

Chapter XVII. How many pairs of cranial nerves are there? of 
spinal nerves? Which roots of the spinal nerves contain the afferent 
and which the efferent fibers ? (This may be fixed in the mind by 
remembering that the first letters of the words dorsal and afferent, 
and of ventral and efferent, spell Dave .) What is the function of the 
sympathetic system ? Explain how a sympathetic reflex is carried 
out. How much sleep is needed by a person of your age ? What 
are the effects of tobacco on the nervous system ? of alcohol ? 

Chapter XVIII. How is alcohol formed? What is its effect on 
length of life? on the death rate from tuberculosis? What per cent 
of insanity is caused by alcohol? Give some facts that show that the 
evil effects of alcohol are inherited. Speak of the effects of alcohol 
on the character. 

Chapter XIX. Name the special senses. How is the sensation 
of feeling caused? of taste? of smell? How may the olfactory cells 
be injured? How does a wave in the air cause a sensation of sound? 
Mention some ways in which the ears may be injured. Define : 
auditory canal; tympanic membrane ; tympanum ; malleus ; incus; 
stapes ; Eustachian tube; vestibule; cochlea. 

Chapter XX. How is the eye protected? Draw a diagram of a 
longitudinal section through the eye. Explain how an image is 
formed on the retina. Explain how the eye is accommodated. 
What is the trouble in a near-sighted eye? in a far-sighted eye? in 
an astigmatic eye ? In each case what kind of spectacles is needed ? 
Mention some points connected with the hygiene of the eye. 

Define : lachrymal gland ; retina ; vitreous humor; aqueous humor ; 
cornea; iris; pupil; suspensory ligament; ciliary muscles. 

Chapter XXI. Tell how to revive a person who has been under 
water. What should be done in cases of suffocation? of bleeding? 
of fainting? of sunstroke? when the clothing is on fire? in treating a 
burn? in cases of poisoning? 


CHAPTER XXII 


DISEASE GERMS 

Disease germs cause the death of over 50 per cent of the 
human race. In addition to this great loss of life, they are 
responsible for an amount of suffering so great that it can 
hardly be imagined. Every year millions of dollars’ worth of 
time is lost by persons suffering from diseases caused by 
germs; great amounts of time and money are constantly 
being spent in caring for these sufferers; and every year 
hundreds of thousands of people rise from beds of sickness, 
weakened for life by diseases caused by these small enemies 
of mankind. 

A great part of this suffering and loss of money, time, and 
life is unnecessary, for germ diseases are, in the main, pre¬ 
ventable. 1 The most useful facts of all science, therefore, 
are the facts that give us a knowledge of disease germs and 
how to avoid them. 

What are Disease Germs? One-celled animals are called 
protozoa (singular, protozoon ), and one-celled plants of a cer¬ 
tain kind are called bacteria (singular, bacterium). The prin¬ 
cipal breeding places of protozoa and bacteria are in water 
and in the earth. To most kinds of them we pay no attention, 
for they are harmless. A few kinds, however, grow in the 
bodies of man and other animals, and cause sickness. When 

1 “ It is within the power of man to cause all parasitic diseases to disappear 
from the world.” — PASTEUR. 


285 


286 


HUMAN PHYSIOLOGY 


we speak of disease germs, we are referring to the little ani¬ 
mals and plants that grow in the bodies of men and animals 
and cause disease. 

The Multiplication of Disease Germs. All that most disease 
germs do when they multiply is to grow longer and pinch in 
two. Then there are two germs. A cholera germ may be¬ 
come full-grown and divide in twenty minutes, and all disease 
germs multiply with astonishing rapidity. If one germ and 
the germs that come from it should divide at the rate of once 
an hour, in twenty-four hours they would increase to more 
than seventeen millions. 

Where Disease Germs come from. The germ of typhoid 
fever may be in water, the smallpox germ on clothes, the 
diphtheria germ on a pencil or a drinking cup, and the germ 
that causes consumption may be in the dust that blows about 
the streets. These germs, however, do not originate in the 
water, on the clothes or pencil, or in the dust, but in nearly 
all cases they come from some human body in which they are 
growing. In the prevention of germ diseases, nothing is so 
important, therefore, as to keep germs from the bodies of 
persons who have these diseases from being scattered about. 1 
The following experiments will show that disease may be 
spread by allowing the little plants and animals that cause 
them to get into new locations where they can grow: 

1 It is important to realize that germs are plants and animals, and that a germ 
can grow only from another living germ of the same kind. It is unsafe to have 
dirt and unclean matter about, for if germs get into it they may live in it for a 
long time and often may multiply in it; but the idea that germs originate in 
such matter is not correct. As we shall see later, a few germ diseases may occa¬ 
sionally be contracted from animals, and people who are not themselves sick 
may sometimes carry certain kinds of disease germs in their bodies. In most 
cases of germ diseases, however, the germ comes from another person who is 
suffering with the disease. 


DISEASE GERMS 


287 


Thrust a needle into a rotten apple and then into a sound apple. 1 
Lay the sound apple away for a few days and wait for the appearance 
of the disease in it. Cut it open and note how the rot has spread 
out from the needle path. The disease will probably develop more 
quickly if you will bore a small, deep hole in the side of the apple 
and pack some of the rotten material from the apple into it. 

Inquire among greenhouse owners and find a carnation that is 
suffering from stem rot. Cut into the diseased stem, and then with 
the same knife cut a healthy stem half in two. Tie a cloth about the 
wounded stem, and keep it moist until the disease develops. The 
disease may be more surely produced by putting into the wound a 
little matter from the diseased stem. 

How Disease Germs enter the Body. Sometimes disease 
germs enter the body through the skin, working down 
through the hair follicles and sweat glands, or getting into 
wounds. The germs of a number of diseases are introduced 
into the body by the bites of insects. More commonly, germs 
enter the mouth or nose and grow in the walls of the air 
passages, the walls of the alimentary canal, or in the lungs. 
A knowledge of how a germ enters the body often helps us 
to avoid the disease that it causes. 

How Germs cause Sickness. When disease germs grow in 
the body, they produce substances called toxins. The toxins 
are very violent poisons, and cause illness by poisoning the 
cells of the body. You should get clearly in mind the fact 
that it is not the germs themselves , but the toxins that the 
germs produce , that cause the disease. Almost all fevers are 
caused by the toxins of disease germs. 2 

1 Rots are caused by fungi (Fig. 151) that are much larger than the bacteria 
and protozoa that cause diseases in our bodies. The fungi are living plants, 
however, and closely related to the bacteria; and rots are spread by the spreading 
of the fungi that cause them, just as our diseases are spread by the spreading of 
the bacteria and protozoa that cause them. 

2 Within the body, substances called antitoxins are produced to destroy the 
toxins. These are discussed on page 307. 


288 


HUMAN PHYSIOLOGY 


How the Body kills Germs. Germs that get into the body 
are killed in two ways — by the white corpuscles of the blood 
and by a germicidal ( < germ-killing ) substance that is in the 
blood. The white corpuscles flow around the germs and 
take them in, or swallow them. Then the corpuscles 
attempt to digest and kill the germs, and the germs try to 
grow in the corpuscles and use them for food. If the cor¬ 
puscles triumph, the germs will be killed and the disease 



and partially broken up by the corpuscle. 

will be checked. If the germs are victorious, the corpuscles 
will be destroyed, the disease will go on, and the patient will 
finally die. 

Just what the germicidal substance of the blood is or where 
it comes from is not certainly known, but there is something 
dissolved in the blood that kills germs that get into the body. 
The blood of a healthy person always has some germicidal 
substance in it and some power of killing germs. When 
disease germs get into the body, more of this substance is 
manufactured and thrown off into the blood, where it power¬ 
fully aids the white corpuscles in the fight against the germs. 
The turn of the fever in germ diseases comes when the 
corpuscles and the germicidal substance begin to get the 
better of the germs. 

Different Germicidal Substances. There is a different ger¬ 
micidal substance for each different kind of disease germ, and 


DISEASE GERMS 


289 


after recovery from an attack of a disease, a large amount 
of the germicidal substance for the germ of that disease will 
be found in the blood. The germicidal substance for some 
germs remains in the blood for years, and there are many 
diseases that people usually have but once. This is because 
after an attack of one of these diseases the germicidal sub¬ 
stance remains in the blood through life and promptly 
kills any germs of that kind that may get into the body. 
In other diseases the germicidal substances quickly disap¬ 
pear from the blood, and we may have them again and again. 

Inherited Diseases. It is often said that diseases (eg. con¬ 
sumption, leprosy, cancer) are inherited. By this, it is not 
meant that the germs of a disease are inherited, but that 
little power of killing those germs is inherited. If the 
parent has little power of killing a certain germ, the child 
will also be likely to have little power of killing it. The 
germ may get into the body of the parent, and, finding little 
resistance, attack him. At another time it gets into the 
body of the child, and the germicidal power of the blood 
being slight, the child is also attacked. Certain families are 
weak in their power of resistance to certain germs, and 
therefore suffer from the diseases caused by these germs. 
Races of men differ in their power to kill germs, the Mon¬ 
golians particularly being attacked by leprosy, and the 
negro race having little resistance to the germ that causes 
consumption. The germicidal power of the body is inherited 
in races as well as in families, but it is the lack of power to 
kill the germ , and not the germ itself \ that is inherited. A 
member of a family that suffers from a certain disease should 
take special care to keep himself free from the germs of that 
disease, for as long as he can keep these germs out of his 
body, he may be as healthy as any one. 


290 


HUMAN PHYSIOLOGY 


Keeping up the Germicidal Power of the Body. The seeds 
of plants lie in the earth through the cold winter, waiting for 
the warmth of spring to enable them to grow; so disease 
germs often lie in the body, ready, if a favorable time comes, 
to start their growth. Germs capable of producing disease 
are usually in the body, and the germs of most dangerous 
diseases often enter the body at times unknown to us. The 
only safe way, therefore, is' always to keep the body in 
health, so that it may be able to repel any attacks that may 
be made upon it. Overwork, hunger, exposure to cold, wet 
feet, insufficient sleep, bad ventilation, bad food, lack of exer¬ 
cise, alcohol — all of these things injure the body and lower 
its germicidal power. It is a duty that every one owes to 
himself to keep his body in good condition, and to fail to do 
so is no more sensible than it would be for a garrison in a 
hostile country to go to sleep with the gates of the fortress 
open. 

Alcohol and Germ Diseases. We have already learned that 
the world’s greatest authorities on tuberculosis state that al¬ 
cohol drinking renders the body more susceptible to the 
germ that causes that disease (page 240). Physicians have 
observed that a drunken spree sometimes brings on an attack 
of pneumonia, and it has long been the opinion of medical 
men that alcohol drinkers are more liable to the attacks of 
germ diseases than are non-users of alcohol. 

More recently it has been definitely proved by experiments 
on animals that alcohol lowers the germicidal power of the 
body, and it has been discovered that alcohol paralyzes the 
white corpuscles and renders them unable to take up and 
destroy disease germs. Knowing this, it is easy to understand 
why drinking may bring on an attack of a germ disease. 
When pneumonia germs are already in the body waiting for 


DISEASE GERMS 


291 


a chance to attack it, and the white corpuscles are paralyzed 
by drinking alcohol, we need not be surprised if the disease 
develops. 

Summary. Disease germs cause the death of over one half 
of the human race. They are small plants and animals that 
grow in the body and multiply with great rapidity. They 
are spread from the bodies of those who are suffering with 
germ diseases, enter the body in various ways and cause dis¬ 
ease by producing a poisonous toxin. 

The body kills germs by its white blood corpuscles and by 
a germicidal substance in the blood. The germicidal sub¬ 
stance is increased during an attack of a disease, and after 
recovery may remain in the blood, so that the person will be 
protected against that disease for life. Certain families and 
races of men are particularly weak in their power to kill cer¬ 
tain germs. It is of the greatest importance to keep up the 
germicidal power of the body. This is lowered by alcohol. 

QUESTIONS 

What are disease germs? How do they multiply? Where do the 
germs that cause our diseases come from ? How do they enter the 
body ? How do they cause sickness ? How does the body kill them ? 
Why do we usually have certain diseases only once ? What is meant 
by an inherited disease ? Why is it important to keep up the germi¬ 
cidal power of the body? Mention some ways in which the resist¬ 
ance of the body to germs may be lowered. How does alcohol reduce 
the power of the body to kill germs ? 


CHAPTER XXIII 


DISEASES CAUSED BY PROTOZOA 

The protozoa (page 285) are the smallest of all animals. 
The largest of them can barely be seen with the naked eye, 
and under the most powerful microscope the.smallest of them 
look like tiny specks. Some of those living in the ocean have 
shells, and so abundant are they that great beds of chalk and 
limestone are built by them. Others are phosphorescent, 
and in the warmer seas the waves at night are often fringed 
with light from the multitude of protozoa in the water. 
They are abundant in fresh water also, every pool and pud¬ 
dle containing great numbers of them, and they grow as 
parasites in almost every animal from worms and insects up 
to man. Some of our worst diseases are caused by protozoa. 

MALARIA 

Malaria is one of the worst diseases that afflict mankind. 
No community or portion of a country can reach its highest 
state of development as long as malaria is prevalent in it; 
for the disease affects a large number 1 of the inhabitants, 
and persons so affected do not have and cannot have the 
strength, energy, and ambition necessary to carry on great 

1 In malarial countries the germ is sometimes found in the blood of from 20 to 
60 per cent of the inhabitants. In many instances the disease takes a slow 
chronic form in which the patient does not have chills and fever, and often does 
not know that he is suffering from the disease. The germ may remain in the 
body for years. 

292 


DISEASES CAUSED BY PROTOZOA 


293 


enterprises. Many of the most backward portions of our 
country would in a very few years be centers of industry, 
education, and leadership, if malaria could be eradicated from 
them. 

The Cause of Malaria. Malaria is caused by protozoa that 
live in the red corpuscles of the blood. The protozoon in¬ 
creases in size until it almost 
fills the corpuscle. Then 
it divides into a number of 
parts, each of which is a 
young germ. These break 
out of the corpuscle into 
the blood, and then each 
one settles upon and en¬ 
ters a fresh red corpuscle. 

Within the corpuscle the 
germ grows and the young 
break forth in due time to 
repeat the process. 

During their growth 
within the corpuscles the 
malaria germs produce 
toxin. At the time when 
the young break down the 
corpuscles and come out into the blood, a great amount of 
this toxin is liberated in the blood at once, and the result is a 
chill and fever. In addition to injuring the body with its 
toxin, the malaria germ destroys millions of the red blood 
corpuscles, thus interfering with the oxygen-carrying power 
of the blood. 

Kinds of Malaria Germs. There are several different va¬ 
rieties of the malaria germ, some of which produce a more 



Fig. 138. The malaria germ in a red blood 
corpuscle. A, B, and C show the growth of 
the germ; D shows it dividing into a number 
of young germs; E shows the corpuscle 
broken down and the young germs escaping 
into the blood. 



294 


HUMAN PHYSIOLOGY 


severe form of the disease than others. In one form of the 
disease the germ requires seventy-two hours to complete its 
growth and break out of the corpuscles. In this kind of 
malaria, the chill comes every third day. In other forms, the 
germs require forty-eight hours for their development, and 
in these kinds of malaria the chill comes every other day. 
It is quite possible, however, to have more than one crop of 
the germs in the blood at one time. One set of germs may 
break out of the corpuscles one day and a different set the 
next day, so that the affected person may have a chill every 
day. In some cases of malaria the germs jnay keep coming 
out all the time and the patient may have a continuous fever. 
Usually a malarial fever rises and falls, and for this reason 
a continuous malarial fever is often called remittent fever. 

How the Malaria Germ enters the Body. The malaria germ 
is introduced into the body by a certain species of mosquito 
(Fig. 152). A mosquito feeds on man by inserting its pro¬ 
boscis through the skin and sucking out the blood. When a 
mosquito draws blood from a person who is affected with 
malaria, it takes malaria germs into its stomach. The germs 
enter the wall of the mosquito’s stomach, and multiply there, 
and many of them finally reach the mosquito’s salivary 
glands. 

The opening in the proboscis of a mosquito is too fine 
to allow red blood corpuscles to pass through it. The mos¬ 
quito, therefore, when it thrusts its proboscis through the 
skin to feed, injects saliva down through its proboscis into 
the wound to break up and digest the red corpuscles. If 
the mosquito is infected with malaria, the germs will be 
injected into the wound with the saliva. The germs thus 
introduced into the body enter the red blood corpuscles, and 
about a week later the disease develops. 


DISEASES CAUSED BY PROTOZOA ' 


295 


Curing Malaria. After the germs of most diseases get 
into the body, it is impossible to kill them by taking medi¬ 
cines. The germs are harder to kill than our own cells, and 
we cannot poison them with medicines without poisoning our 
own bodies. Fortunately, the human body can endure an 
amount of quinine that will poison and kill the germ of mala¬ 
ria. 1 Malaria is, therefore, one of the few germ diseases that 
can be successfully treated by taking medicine to kill the 
germ. It is far better, however, to prevent the disease than 
to try to cure it. 

The Prevention of Malaria. Man gets the malaria germ 
from the mosquito, and the mosquito gets it from man. If we 
could destroy all mosquitoes, the disease, of course, would die 
out. If we could destroy all the germs that are in the blood 
of malaria patients, the mosquitoes would not become infected, 
and the disease would cease to be spread. The following 
suggestions for the prevention of malaria are in accordance 
with these principles, and by following them out much can be 
done to check the disease: 

Screening Malaria Patients. It is very important to keep 
a malarial patient under mosquito netting until the germs dis¬ 
appear from his blood. Where this is not done, it has been 
found that the mosquitoes in the house become infected by 
biting him, and that other persons in the house usually 
contract the disease. In regions where there is only an 
occasional case of malaria, or where only a few persons are 
living close together (as in a country farmhouse), this pre¬ 
caution will do much to prevent the spread of malaria. 

Avoiding Unnecessary Exposure to Mosquitoes. Persons 

1 Malaria germs are killed much more easily by quinine while they are free in 
the blood than when in the corpuscles. The quinine should be taken so that it 
will be in the blood at the time when the germs come out of the corpuscles. 


296 


HUMAN PHYSIOLOGY 


living in malarial regions should keep their houses carefully 
screened and should sleep under mosquito nets during the 
mosquito season. They should not expose themselves to the 
attacks of mosquitoes very early in the morning or late in the 
day, and should take care to avoid the haunts of the mosqui¬ 
toes on cloudy days when mosquitoes are flying. Judgment 
should be exercised in selecting places to be visited in camping 
and fishing excursions, for one night spent among mosquitoes 
may start an attack of malaria that will last for months. 

The Use of Quinine. Quinine frees the blood from malaria 
germs, and thus prevents mosquitoes from becoming infected. 
A little quinine in the blood will also kill any malaria 
may be introduced into the body by an infected 
mosquito, and thus prevent the development of 
the disease. In malarial regions it is sometimes 
advisable to take small doses of quinine daily 
as a preventive measure. 

Destroying Mosquitoes . This is the most 
effective of all the measures that are employed 
in fighting malaria. The subject will be dis¬ 
cussed in a later chapter (page 323). 

DYSENTERY 

Chronic dysentery is usually caused by a pro- 
tozoon, an amoeba , that is similar in many ways 
to a large white blood corpuscle. The disease 
is most common in the tropics, but is found in 
our own country. The amoeba of dysentery lives 
in water, and when swallowed, enters the wall 
of the large intestine and grows there. The 
disease comes from impure water, and the best methods of 
preventing it will be taken up in another chapter. 


germs that 



Fig. 139. 

The amoeba 
of dysentery. 
The three dark 
bodies within 
the amoeba 
are red blood 
corpuscles on 
which it has 
been feeding. 





DISEASES CAUSED BY PROTOZOA 


29 7 



SMALLPOX GERM 


Fig. 140. The germs of 
smallpox in the cells of 
the skin. 


SMALLPOX 

Smallpox is probably caused by a small protozoon that 
lives in the cells of the skin and of certain other parts of the 
body. 1 The germs may be carried on 
clothing or anything that a smallpox pa¬ 
tient touches, and there are great numbers 
of germs in the dried scales that come from 
the skin during recovery from the disease. 

As smallpox germs may remain alive for 
months after being dried and scattered, 
the disease is very easily spread. For this 
reason a person suffering from smallpox should be quaran¬ 
tined, and everything that has been about him should be 
burned or disinfected (page 332). The incubation period of 
smallpox (the time between the entrance of the germs into 
the body and the appearance of the disease) is usually from 
ten to twelve days. 

Vaccination. Before vaccination was discovered, smallpox 
was one of the hardest of all diseases to control. Up to a 
little over one hundred years ago, about 95 per cent of all 
persons were attacked by it, and the number of deaths from 
smallpox was enormous. About the year 1800 vaccination 
began to be practiced, and in all civilized countries it is now 
more or less compulsory. Where vaccination is thoroughly 
carried out, smallpox has almost ceased to exist, but in coun¬ 
tries where the people are not vaccinated, or where only part 


1 There is still some uncertainty in regard to the germ of smallpox, some of 
those who have studied the bodies shown in Figure 140 holding that they are not 
the germs that cause the disease. It is certain, however, that smallpox is a 
germ disease, and we have learned how to control it even if we are not certain 
as to the exact germ that causes it. 


298 


HUMAN PHYSIOLOGY 


■ 1 


of them are vaccinated, it is still impossible to prevent the 
spread of the disease . 1 

How Vaccination protects against Smallpox. The germ of 
smallpox flourishes in man. It grows in cattle also, causing 
the disease called cowpox. After growing in the cow this 
germ seems to be weakened and changed so that it grows 
feebly in man and has only a slight power of producing 
disease. 

In vaccination, germs from a cow are put into the human 
body. Here they grow and begin to produce the mild inflam¬ 
mation that follows vaccination. The body now works up the 
germicidal substance for these germs and kills them out 
before they can make much growth and spread through the 
body. After this is done, the germicidal substance remains 
in the blood, and if any smallpox germs get into the body, the 
germicidal substance is there to kill them. 

From this you will understand that a person who has been 
successfully vaccinated is in very much the same condition 
as a person who has had a light attack of smallpox. After 

1 In 1874 Germany passed a compulsory vaccination law requiring that every 
child be vaccinated within a year after birth, and that every pupil in an educa¬ 
tional institution be vaccinated between the ages of thirteen and fourteen years. 
Under this law, from 1893 to 1898 Germany had 287 deaths from sm&llpox. 
During this time there were many epidemics of smallpox in other European 
countries where only part of the people had been vaccinated. In the same five 
years Russia had over 275,000 deaths from the disease, Spain nearly 24,000, 
Hungary over 12,000, and Italy and Austria each over 11,000. Before the 
American occupation of the Philippine Islands, only a part of the inhabitants of 
the Islands had been vaccinated, and thousands of deaths from smallpox occurred 
every year. The people have now been thoroughly vaccinated, and in 1907 there 
was not a single death from the disease in seventeen provinces of the Islands. 
There is no doubt that the decrease in the death rate is due to vaccination, for 
quarantining has failed to prevent a considerable amount of certain other diseases 
(diphtheria- scarlet fever, etc.) that are much less contagious than smallpox. 


DISEASES CAUSED BY PROTOZOA 299 

vaccination, as after recovery from an attack of many germ 
diseases, the germicidal substance in the blood becomes 
weaker and weaker, but never entirely disappears. Just when 
it becomes so weak that revaccination is necessary, it is im¬ 
possible to say. A successful vaccination usually protects 
from smallpox for several years. Sometimes the germicidal 
substance in the blood is fairly strong after seven, eight, 
nine, or ten years. Two successful vaccinations usually 
protect against smallpox for life, but in a very few persons 
the germicidal substance disappears so rapidly after vaccina¬ 
tion that the disease may be contracted in nine months. The 
safest way is to be vaccinated every few years, and when 
smallpox is prevalent, to be revaccinated if more than nine 
months have passed since the last vaccination. There can 
be no mistake in this, for if the germicidal substance is still 
strong in the blood, all the germs put in by vaccination will 
be killed, and the vaccination will not take. If the vaccina¬ 
tion does take, it is a sure sign that the germicidal power of 
the body had run low and that revaccination was needed. 


RABIES (Hydrophobia) 

Rabies is believed to be caused by a protozoon that grows 
in the nerve tissue. This germ attacks not only man, but 
also many of the lower animals. It is found in the saliva of 
animals suffering from the disease, and usually gets into t.ie 
human system through the bites of rabid animals. Practically 
all the rabies in our country comes from the bites of dogs, 
and it would be possible by properly muzzling dogs to stamp 
out the disease entirely, as has been done in several Eu¬ 
ropean countries. It is a mistake to think that rabies de¬ 
velops in dogs because of hot weather, for they get the 


300 


HUMAN PHYSIOLOGY 


germ from the bites of other dogs and may have the disease 
at any time of the year. 

In man the germ of rabies grows very slowly. At least 
two weeks are required after the germs are introduced 
into the body before the disease shows itself. Usually the 
disease does not develop for five or six weeks, and some¬ 
times not for a year. There is no cure for rabies after the 
disease develops, but a preventive treatment, founded on the 
same principles as vaccination, was discovered by a great 
French scientist named Louis Pasteur. The Pasteur treat¬ 
ment is successful in nearly all cases in which it is com¬ 
menced in time. Where the materials for this treatment can 
be delivered within thirty-six hours, they can be sent by mail 
and the treatment given to the patient by his home physician. 
No time should be lost in beginning the treatment. 

The Treatment of Wounds made by Rabid Animals. A 
very great safeguard against this disease is to treat promptly 
wounds made by the teeth of animals with something that 
will kill the germs in the wounds. Any disinfectant (page 
334) is useful, but burning with nitric acid is the most effec¬ 
tive remedy. This should be done by a physician to make 
sure that it is thoroughly done, and to guard against too great 
injury to the flesh by the acid. The best method is to apply 
at once to the wound any disinfectant that may be at hand 
and then have it treated as soon as possible by a physician. 
Treatment of the wound even after twenty-four hours is 
useful. An animal that has bitten any one should not be 
killed, but should be confined until it is known whether or 
not it has hydrophobia. If the animal remains in health for 
nine or ten days, there will then be no occasion for worry. 

Other Protozoan Diseases. In the tropics many diseases of 
man are caused by protozoa. Among these diseases are the 


DISEASES CAUSED BY PROTOZOA 


301 


slow and fatal sleeping sickness of Africa, which is commu¬ 
nicated to man by a fly. It is thought that scarlet fever, 
measles, and possibly cancer, are caused by protozoa, but 
these diseases are not thoroughly understood. Rocky Moun¬ 
tain or “spotted” fever, a disease of the Rocky Mountains, 
which is caused by the bite of a tick, is almost surely a 
protozoan disease. A protozoon that is carried by a tick 
causes the “Texas fever” or “tick fever” that is prevalent 
among cattle in our Southern states, and in the tropics many 
fatal diseases of animals are caused by protozoa. 

Summary. Protozoa cause many diseases of man. 
Among them are malaria, dysentery, smallpox, and rabies. 
The germs of malaria are carried by the mosquito, and the 
disease may be escaped by avoiding mosquitoes. Dysen¬ 
tery usually comes from impure water. The germ of 
smallpox is easily spread, and few persons naturally have 
the power to resist it. By vaccination the germicidal 
power of the body toward the smallpox germ may be 
raised and the disease controlled. Rabies comes from the 
bites of dogs. Generally the disease can be prevented 
from developing by the Pasteur treatment. Wounds made 
by the teeth of animals should be disinfected. Protozoa 
cause other diseases of animals and men. 


QUESTIONS 

Why is malaria an important disease? Describe the life history 
of the malaria germ. What causes the chill in malaria? How 
does the malaria germ enter the body? How long is it after the 
germ gets into the body before the disease appears? How may the 
malaria germ be killed in the blood? How may malaria be pre¬ 
vented? Where does the germ of dysentery grow in the body? How 


302 


HUMAN PHYSIOLOGY 


does it get into the body ? How may smallpox germs be spread ? 
What is the incubation period of the disease? What per cent of 
people had smallpox before vaccination was practiced? Explain 
how vaccination protects the body. How often should one be 
vaccinated ? 

How does the germ of rabies enter the body ? How may the 
disease be stamped out? What is the incubation period of 
rabies? How may the development of the disease be prevented? 
How should wounds made by the teeth of animals be treated? 
Name some other diseases that are thought to be caused by pro¬ 
tozoa. 


In some parts of our country there is no malaria. Why is this the 
case ? Sometimes persons who have been living in a malarial region 
have chills and fever when they move into a region where there is no 
malaria. In such cases, where do the germs come from that cause 
the disease? People sometimes have chills and fever in the winter 
or spring when no mosquitoes are flying. Where do the malaria 
germs come from in these cases? 

When persons who have been vaccinated take smallpox, they 
usually have a light attack of the disease. Why should you expect 
this to be the case? Ask a physician to explain to you the Pasteur 
treatment for hydrophobia. How does the principle underlying this 
treatment resemble the principle on which vaccination is founded? 

With a microscope examine a drop of dirty water for protozoa. 



CHAPTER XXIV 


DISEASES CAUSED BY BACTERIA 

Bacteria are so extremely small that millions of them 
have plenty of room to swim about in a drop of water, and 
a drop of sour milk commonly contains about fifty million 
bacteria. It would require twenty-five thousand of them, 
placed side by side, to make a row an inch long. Examined 
under a microscope that would cause a man to appear as 
high as Mount Washington or Mount Mitchell, bacteria look 
about as large as the periods and commas in ordinary print. 
So exceedingly small are these little plants that they can 
pass through the pores in a brick as easily as a man passes 
through the doorway of a house. 

Another remarkable thing about bacteria is their power of 
multiplication. It has been calculated that if all the bacteria 
in the world could get food, warmth, and moisture so that 
they could multiply as fast as they are capable of doing, in 
two days they would fill all the oceans and cover all the land 
fifty feet deep. Fortunately for us, most of them are held in 
check by lack of the right conditions for growth. Yet they 
show what they can do when they get into such favorable 
places as warm milk; for a quart of milk, before it sours and 
thickens, usually contains eight or nine hundred billions of 
bacteria. 

The Distribution of Bacteria. Bacteria are everywhere 
about us — in the water, in the soil, and clinging to the small 

303 


304 


HUMAN PHYSIOLOGY 


particles of matter that are always floating about in the air. 
About three million bacteria are ordinarily found in an ounce 
of cultivated soil, and they are much more abundant than 
this in the earth around houses and barns. The water from 
most wells contains more than one million bacteria to the 
quart. Millions of bacteria are always growing on the hu¬ 
man skin, and in the mouth, the intestine, and the respiratory 
passages. Some kinds of bacteria are useful; most kinds are 
harmless, and to them we pay no attention; but a few kinds 
produce toxins in the human body that cause some of our 
worst diseases. 

Shapes of Bacteria. Bacteria are cylindrical, spherical, or 
spiral—shaped like a firecracker, a marble, or a corkscrew. 

The cylindrical bacteria are called 
bacilli (singular, bacillus ). The 
spherical bacteria are called cocci 
(singular, coccus ), and the spiral 
forms are called spirilla (singular, 
spirillum). The shapes of bac¬ 
teria have nothing to do with the diseases which bacteria 
cause, but often give a convenient way of distinguishing 
between different kinds. 


Fig. 141. Bacteria. A is a ba¬ 
cillus, B is a coccus, and C is a 
spirillum. 


BACTERIAL DISEASES OF THE RESPIRATORY ORGANS 

Diphtheria. The diphtheria germ grows usually in the 
pharynx, but is also commonly found in the larynx and 
mouth, is sometimes found on the lips and in the nose, and 
may grow in other parts of the body. It does not usually 
grow outside of the human body, but it can remain alive for 
several weeks in matter that has come from the throat of 
a diphtheria patient. On slate pencils that have touched the 


DISEASES CAUSED BY BACTERIA 


305 


lips of a person who has diphtheria, living diphtheria bacilli 
have been found for several days. The incubation period 
of the disease is usually from two to seven days, but may 
be less. 

Sometimes attacks of diphtheria are so severe that death 
comes in a day or two. In other cases, the germs make only 
a slight growth before the body gets the upper hand of them, 
and the attack is so light that it is often mis¬ 
taken for a simple case of sore throat. In 
still other cases, the diphtheria bacillus lives 
in the throat without causing illness at all. 1 
Where the germs remain in the throat without 
causing sickness, the body is able to hold them fig. 142. The 
in check and keep them from making enough j^P hthena baciU 
growth to harm it, but is not able to kill them 
out entirely. After recovery from an attack of diphtheria it 
is not uncommon for virulent germs to be found in the throat 
for four or five weeks, and in one case they were found eight 
months after recovery from the disease. The disease called 
membranous croup is the same as diphtheria. 

How Diphtheria is contracted. Diphtheria is usually con¬ 
tracted by inhaling the germs. Frequently germs that have 
been coughed out into the air 2 by a person who has the bacil¬ 
lus of diphtheria in his throat are inhaled. Dried sputum 

1 Most healthy persons who have the diphtheria germs in their throats have 
been about some one who is suffering from the disease. 

2 In coughing, sneezing, laughing, and to a certain extent in talking, small 
droplets of liquid are sent out into the air. These may fly to a distance of three 
feet, and some of them are so very fine that they are said to float in the air for as 
long as twenty minutes. When a person is suffering from a disease like diphthe¬ 
ria, pneumonia, or consumption, these droplets are of course filled with the germs 
of the disease. One should not stand near a person who is coughing, and a sick 
person should hold a handkerchief before his face when he coughs. 



30 6 


HUMAN PHYSIOLOGY 


which contains diphtheria germs may spread the disease by 
being blown about as dust and inhaled. The germs are 
almost certain to get on the handkerchiefs and hands of 
persons having the disease. They may be left on a drinking 
cup or on a pencil, on a toy or a piece of candy that has 
been handed about among children, and in many other ways 
they may be transferred from one person to another. They 
sometimes get into the body from milk (page 330) and they 
are often carried by flies and left where they reach the 
respiratory passages. 

Quarantining in Cases of Diphtheria. The diphtheria germ 
is sometimes found in the throats of healthy persons, in the 
throats of diphtheria patients who have long since recovered 
from the disease, and in mild diphtheria cases where the disease 
has not been recognized. Persons are therefore going about 
who are themselves perfectly well, or at least only slightly ill, 
but who nevertheless carry diphtheria germs that are exceed¬ 
ingly dangerous to others. These persons usually object to 
being quarantined, and health officials have great difficulty in 
preventing the spread of diphtheria. The only way by which 
the disease can really be controlled is to shut up in quarantine 
every one who has virulent diphtheria germs in his throat, 
whether or not he is himself ill. This often involves quaran¬ 
tining for long periods of time both diphtheria patients and 
members of families in which there is diphtheria. 

Diphtheria Toxin and Antitoxin. The diphtheria germ may 
cause death by closing the throat, but usually the cause of 
death is the very powerful toxin which the germ produces. 
This toxin attacks the nervous and the muscular systems, 
and the direct cause of death often is that the nerve and 
muscle cells of the heart are so injured that the heart stops. 

We have already studied about how, when germs get into 


DISEASES CAUSED BY BACTERIA 


30 7 


the body, the body begins to work up its power of killing 
them. So when toxin is produced in the body, the body 
works up a substance called antitoxin that neutralizes, or 
destroys, the toxin. If the body can produce enough anti¬ 
toxin to keep the toxin from poisoning the cells, the germi¬ 
cidal power of the blood will rise, and finally the germs will 
be killed out. But if the toxin is not destroyed, it will poison 
the body and take away its power of killing germs, the bac¬ 
teria will triumph, and death will come. The antitoxin does 
not kill the germs , but protects the body from the toxin until 
the white corpuscles and the germicidal substance in the blood 
can overcome the germs. 

The Antitoxin Treatment. It was found that the horse 
has a very great power of producing antitoxin, and the anti¬ 
toxin now constantly used in the treatment of diphtheria is 
secured from the horse in the following way: 

Diphtheria germs are placed in beef broth, where they 
grow and multiply, and produce great amounts of toxin. A 
little of this toxin is then injected into the blood of a horse, 
and the horse works up antitoxin to destroy it. Then a 
larger dose of toxin is given the horse, and still more anti¬ 
toxin appears in the blood. This is kept up until the blood 
is made as strong in antitoxin as possible. Then the horse 
is bled, and the blood allowed to coagulate, or clot. The 
thin, yellowish serum that appears around the clot contains 
the antitoxin, and it is this which is placed in sealed bottles 
and sold as antitoxin after it has been freed from certain 
slightly injurious substances which it contains. 

When a person has diphtheria, and the germs 'begin to 
manufacture toxin and poison the cells, some of the antitoxin 
from the horse is injected into the blood. This unites with 
the toxin and saves the body cells from being poisoned, thus 


308 


HUMAN PHYSIOLOGY 


giving the body time to kill out the germs and so to stop the 
disease. When antitoxin is used in the early stages of the 
disease, the death rate is only about one fourth as great as 
when it is not used. But it is very important to use it early, 
for after the toxin has already poisoned and destroyed the 
cells, it is too late for the antitoxin to be used with much 
benefit. It is useful, however, in all stages of the disease, 
and when a person has been exposed to diphtheria is often 
given as a preventive of the disease. 

Pneumonia. Pneumonia is caused by a small coccus grow¬ 
ing in the lungs. This germ grows not only in the lungs and 
_. . . air passages, but quite frequently, especially 

i ' • ' m children, g ets i nto th e tympanum and 
causes inflammation of the middle ear. 1 It 
may also cause meningitis (page 317), and 
it attacks many animals as well as man. 

In the colder parts of our country pneu¬ 
monia causes more deaths than any other 
disease — more even than consumption. The germs can sur¬ 
vive more drying and sunlight than diphtheria germs, and are 
more frequently in the air. They are scattered about in the 
same ways that diphtheria germs are scattered, for the sputum 
of a pneumonia patient is filled with the germs. The germi¬ 
cidal substance which is worked up by the body to kill the 
pneumonia germ stays in the blood only a short time, and a 
person may have the disease again and again. So quickly 


it 




Fig. 143. The pneu¬ 
monia germ. 


1 Inflammation of the middle ear is caused by many different kinds of germs. 
It is very serious, for incurable deafness will follow the breaking down of the chain 
of bones, and there is danger of the inflammation spreading. Sometimes the 
germs get into the cavities that are in the bone above the middle ear (Fig. 119), 
producing the disease called mastoiditis , and sometimes they work through into 
the cranial cavity and cause meningitis. Running ears and other diseases of the 
ear from which children especially suffer should not be neglected. 


DISEASES CAUSED BY BACTERIA 


309 


indeed does this germicidal substance disappear from the 
blood that the patient may have a relapse before he has 
completely recovered from an attack of the disease. 

Preventing Pneumonia. It is not advisable to expose one’s 
self unnecessarily to pneumonia germs, for the germs fresh 
from a pneumonia patient are often very vigorous and power¬ 
ful in producing the disease. It is not possible, however, to 
avoid entirely the pneumonia germ, for it is common in the 
air, and a very great number of people — probably more than 
half of those living in colder climates — are carrying it in 
their throats. All of us are sure at some time to inhale it, 
and the best preventive is to keep up the health when pneu¬ 
monia weather comes, so that the body will be able to kill 
out any germs that may find their way to the lungs. This 
is done by avoiding all exposure to cold and wet, avoiding 
alcoholic drinks, taking plenty of sleep and exercise, and 
spending as much time as possible in the fresh air. Any¬ 
thing that builds up the general health is a safeguard against 
pneumonia, and anything that weakens the body may bring on 
the disease, for the pneumonia germ is already in the throats 
of millions of people, waiting for something to lower the germi¬ 
cidal power of the body so that it can grow unchecked and 
cause the disease. An important safeguard is to destroy 
carefully the sputum from a pneumonia patient (page 336). 

Influenza or Grip. Influenza is caused by a very small 
bacillus that grows in the respiratory passages. The grip 
bacilli spread in much the same ways as do the germs of 
diphtheria and pneumonia, but the grip germs die much 
more quickly from drying than either of the others. They 
linger for a long time — sometimes for more than a year — 
in the nose and bronchial tubes of those who have had the 
disease, and are often found in those who have bronchitis 


3io 


HUMAN PHYSIOLOGY 


and consumption. No attempt is made by public officials to 
quarantine grip patients; in families there is usually little 
care taken to keep the germ from those who have not taken 
the disease; and grip germs are, therefore, spread everywhere. 
In grip epidemics a large portion of the population suffers, 
one third of all the people in Chicago having 
the disease at one time in January, 1908. 

The grip germ produces a toxin that has a 
very profound effect on the body. It does not 
poison the body so acutely as the diphtheria 
toxin does, but causes a weakness and a de¬ 
pression that often last for months. Grip also often brings on 
other troubles, such as pneumonia, eye and ear diseases, and 
colds, and it frequently leaves parts of the body, like the kid¬ 
neys, the stomach, or the nervous system, in a weakened and 
diseased condition. Because of these after-effects, because 
it attacks so many people, and because one may have grip 
again and again, influenza is a much-dreaded disease. 

Catarrh and Colds. In catarrh and colds many kinds of 
germs grow in the respiratory passages, and it is not always 
easy to tell which one is causing the trouble. It seems prob¬ 
able that these diseases are caused, sometimes at least, by the 
same germs that at other times cause pneumonia and influ¬ 
enza. This would not be so strange as it may seem, for we 
know of other instances of one germ causing several diseases 
that seem to be very different (page 311). It is practically 
certain that colds are caused by germs, for colds often run in 
epidemics, and epidemics can be explained only on the theory 
that a germ that is transferred from one person to another is 
causing the disease. 

Whooping-Cough. Whooping-cough is undoubtedly a germ 
disease, but nothing is known of the germ that causes it. 



Fig. 144. * The in¬ 
fluenza bacillus. 


D/S EASES CAUSED BY BACTERIA 


311 

Consumption. Consumption is so important a disease that 
it will be discussed in a separate chapter (chapter XXVI). 

DISEASES CAUSED BY BACTERIA THAT ENTER THE BODY 
THROUGH THE SKIN 

The Pus-forming Bacteria. Several different kinds of 
bacteria are included in this group. They are found in earth 
around the habitations of men 
and animals and in polluted 
water, and are always found 
on the human skin, where 
they feed on the dead cells 
and other matter on the skin. 

When they grow in the tissues, 
they cause inflammation and 
form pus , or the thick liquid 
matter that is found in boils 
and infected wounds. 

Diseases caused by the Pus¬ 
forming Bacteria. The pus-forming bacteria cause boils, 
carbuncles, erysipelas, blood poisoning, and inflammation in 
wounds and sores. They may also cause inflammation in the 
internal parts of the body. Tonsilitis and appendicitis are 
usually caused by these germs, and meningitis may be caused 
by them. It thus appears that the same germ that makes a 
wide-spreading growth in the skin and causes erysipelas, can 
make a deep, localized growth and cause a boil or carbuncle, 
spread through all the body and bring on blood poisoning, or 
produce spinal meningitis by growing in the membranes and 
fluids around the brain and cord. The pus-forming germs 
found in cases of erysipelas and abscesses are often very 
malignant, and care should be used to prevent their spread. 


It 


FIG. 145. Three pus-forming bac¬ 
teria. A causes the bluish-green pus 
sometimes found in wounds; B is the 
most common cause of boils; and C 
causes erysipelas and often is the cause 
of boils and of blood poisoning. 




312 


HUMAN PHYSIOLOGY 


The Pus-forming Germs Injurious to the Body. A strange 
idea that is very prevalent is that boils are beneficial to us. 
Probably this belief arises from the fact that so much 
offensive matter comes from a boil. It is exceedingly im¬ 
portant to open up infected wounds, boils, and carbuncles, 
and get the matter in them out of the body, for it is injurious 
and dangerous to allow it to be carried through the body by 
the blood. The pus, however, is composed chiefly of germs, 
dead tissue cells, and dead white corpuscles which the germs 
have killed. It no more benefits the body to have pus¬ 
forming germs kill patches of the tissue and poison the 
whole system with their toxins than it benefits the body to 
have diphtheria, typhoid, or any other disease germs in it. 

Care of Wounds. For our protection against pus-forming 
germs, it is very important to know how to care for small 
wounds. If the wound has been made by a clean instrument, 
and bleeds freely, the blood will wash the germs outward, 
and by its germicidal power will probably kill any bacteria 
remaining in the wound. In such a case, the best thing is to 
tie the wound up “in the blood,” and not open it until it 
is healed, unless inflammation sets in. A good plan is to 
wrap the wounded part in a thin, clean inner cloth, and out¬ 
side of this tie a second cloth. The outer cloth can be changed 
from time to time when it becomes soiled, while the innei 
cloth is left undisturbed to keep germs from getting into the 
wound. 

When a wound has been made with anything unclean, it 
should be washed with a disinfectant (page 335) to kill germs 
in it, before it is tied up. After being bandaged, a wound 
should be carefully watched, and if pain, redness, and swelling 
show that germs have got into it, it should be opened at 
once and disinfected. A salve containing carbolic acid is 


DISEASES CAUSED BY BACTERIA 


313 




very useful in dressing small wounds and sores, because the 
carbolic acid kills germs. Turpentine is an excellent agent 
with which to treat a wound, and one that is often at hand. 

Rheumatism. Acute rheumatism is a germ disease. Some 
think that it is caused by pus-forming bacteria growing in the 
joints, and others hold that it is caused by a very tiny germ 
of its own. When this disease attacks the valves of the 
heart, it is often fatal. 

Tetanus (lockjaw). Tetanus is caused by a bacillus that is 
commonly found in the earth about dooryards and gardens, 
in the dust of streets, and in great abundance 
about stables where horses are kept. It affects 
chiefly man and the horse and gets into the 
body through wounds, often through wounds 
so small and insignificant that no attention 
is paid to them. The tetanus germ by itself fig. 146. 
cannot grow except when it is shut off from The baclIlus of 

, . .... , , , . tetanus. 

the air. With other germs, however, it can 
grow in an open wound. 

The tetanus bacillus grows especially in wounds made by 
unclean instruments, because such wounds are likely to be 
infected with this germ, and because pus-forming germs and 
particles of dirt are left in such wounds. It grows best of 
all in small, deep wounds like those caused by an unclean 
nail, because wounds of this kind readily close over and 
leave the tetanus germ with other germs and foreign matter 
buried deep in the flesh and away from the air. The percus¬ 
sion caps used on toy pistols also make dangerous wounds. 
The germs are in the dust on the skin, and the very small, 
sharp, flying particles of the caps cut deep into the flesh and 
drive down tetanus germs along with other bacteria and dust. 

The bacillus of tetanus is so common that it undoubtedly 


314 


HUMAN PHYSIOLOGY 


gets into many wounds in which it never grows, but it is 
always wise to look after and protect every wound. Wounds 
made by unclean instruments should be carefully sterilized, 
and wounds on the feet of barefooted children should re¬ 
ceive special attention, because these come in contact with 
the earth and are exposed to infection. Wounds of a kind 
that are especially liable to cause the development of the 
disease should be looked after by a physician. 

The Toxin of Tetanus. The tetanus germ makes only a 
very slight growth in the body, but it produces a toxin of tre¬ 
mendous power. This toxin for man is a poison nineteen 
times as strong as dried cobra venom, and two hundred and 
fifty times as strong as strychnin. It produces its effects 
by poisoning the nervous system, and through this so affects 
the muscles that they are all thrown into contraction. The 
muscles of the jaw, esophagus, and neck are often affected 
before the other muscles in tetanus. 

Tetanus Antitoxin. An antitoxin for tetanus has been pre¬ 
pared, but this is successful only when used in large doses 
very soon after the disease develops. It is very useful, how¬ 
ever, in preventing tetanus, and when a person has received 
a wound that is likely to bring on this disease, many physi¬ 
cians make a regular practice of giving a dose of tetanus anti¬ 
toxin to keep the disease from developing. 

Leprosy. Leprosy is caused by a slow-growing bacterium, 
similar in some ways to the tuberculosis germ. It produces 
little toxin, and may exist in great numbers in the tissues of 
the body for years before death results. There is no cure for 
leprosy, and it is slightly contagious, though not so conta¬ 
gious as consumption. 

Bubonic Plague. Bubonic plague is the disease that was 
galled the Black Death in the Middle Ages. In 1907 there 


DISEASES CAUSED BY BACTERIA 


3l5 


were over a million cases of plague and 860,000 deaths from 
it in India. It is caused by a bacillus that gets into the body 
through wounds or through the bites of fleas, lice, or other 
insects. It produces a violent toxin, and about 85 per cent 
of those attacked by it die. This disease also attacks rats 
and mice, and is spread from house to house, or from one 
country to another by rats and the fleas which the rats carry. 

BACTERIAL DISEASES OF THE ALIMENTARY CANAL 

Typhoid Fever. This disease is caused by a bacillus that 
is taken into the body through the mouth, usually in water or 
food. It grows most commonly in the 
wall of the small intestine, but is some¬ 
times found in other parts of the body. 

Sometimes an attack of typhoid fever is so 
light that the patient does not realize that 
there is much the matter with him. Usu¬ 
ally it is a very severe disease, and often 
leaves the sufferer weakened in some or¬ 
gan for life. The excretions from the in¬ 
testines and kidneys of a typhoid patient 
are filled with the germs. 1 These germs can grow in water 
and in refuse matter outside of the body, but if they are 
dried, they die in a very short time. 

How Typhoid is contracted. Since the typhoid germ dies 
from drying, it is not carried about in the air, but must get 

1 About one person in every thirty who has typhoid fever carries the typhoid 
bacillus through life. The germs remain in the gall bladder and intestine with¬ 
out seeming to affect the person in whom they are growing. A cook in New 
York City infected twenty-six persons in a period of five years, and the germs 
have been found in the excretions from the body forty-two years after recovery 
from the disease. 



Fig. 147. The ba¬ 
cillus of typhoid fever. 
This germ is fitted for 
life in the water and 
swims actively. 


316 


HUMAN PHYSIOLOGY 


to the mouth without being dried out. Persons in the same 
house with a typhoid patient may contract the disease from 
the dishes, by getting the germs on the hands, from han¬ 
dling the bedding, or in any of the many ways by which it is 
possible for such small bodies as bacteria to be carried about. 
Flies will carry the germs about in great numbers, if all 
wastes from typhoid patients are not carefully destroyed. 
Occasionally the germ is in oysters that have been grown in 
polluted waters, and for this reason, cooked oysters are safer 
than raw oysters. In a large number of cases, the typhoid 
germ has been carried in milk where some one having the 
disease had prepared or handled the milk , 1 or where the milk 
vessels had been washed in water containing the germs. 
If a single typhoid germ should get into a can of milk, it 
could produce thousands or perhaps millions of germs before 
the milk was used, so the milk supply must be carefully 
watched. In the majority of cases, however, 
typhoid is contracted direct from water. In 
the next chapter we shall discuss the subject 
of disease germs in drinking water. 

Cholera. Cholera is caused by a germ that 
grows with great rapidity in the intestines, 

r IG. 148. The 

cholera germ. and produces a strong toxin, sometimes causing 
death within a few hours. Like the typhoid 
germ, it gets into the alimentary canal through water and foods. 

Other Bacterial Diseases of the Alimentary Canal. There 
is a group of germs closely related to the typhoid germ that 
cause intestinal diseases. The worst of these are the germs 
that cause so much sickness among small children during the 
summer months (Appendix B). 

1 In the spring of 1908 one milkman in Boston who was suffering from typhoid 
caused an epidemic of about 400 cases. 



DISEASES CAUSED BY BACTERIA 


317 


OTHER BACTERIAL DISEASES 

Epidemic cerebrospinal meningitis is caused by a germ that 
grows in the membranes and fluid around the brain and spinal 
cord. The germ is found in the nasal secretions 
of those suffering from the disease. It is thought 
that spinal meningitis is contracted by inhaling 
the germ into the nose, whence it finds its way 
to the brain. The disease is contagious and care 
should be used to prevent its spread. The pneu¬ 
monia germ, the influenza germ, the germ of 
tuberculosis, and one of the pus-forming germs 
may also grow around the brain and cord and 
cause meningitis, but the common contagious form of the dis¬ 
ease is caused by the germ shown in Figure 149. 

One form of soi'e eyes is caused by a bac¬ 
terium. The germs are carried by flies and 
may be wiped on books, doorknobs, or any¬ 
thing which a sufferer from the disease 
touches. Children with this disease should 
not be allowed to attend school, for it is highly 
contagious. It is never quite safe to wash 
the eyes in a public basin, or to wipe them 
on a towel that the public has used. 

Yellow fever , chicken pox , mumps , measles, and German 
measles are certainly germ diseases, but the germs that cause 
them have not been discovered. 1 Many tropical diseases are 
due to either bacteria or protozoa. 

1 The incubation periods of some of the more common infectious diseases are 
as follows: chicken pox, usually 13 to 14 days, but may be 18 or 19 days; mumps, 
13 to 21 days, though it may be shorter; measles, about 8 days; German measles, 
from 2 to 3 weeks; scarlet fever, 2 to 5 days; whooping-cough, about 6 days. 


v/ 
/ / 


w 


Fig. 150. The 
bacillus that 
causes conta¬ 

gious sore eyes. 


s * 


e 9 




Fig. 149. 
The germ of 
cerebro - spinal 
meningitis. 



3i8 


HUMAN PHYSIOLOGY 


Bacteria affecting Animals. Among bacterial diseases of 
animals are hog and chicken cholera, distemper and glanders 
in horses, blackleg in cattle, an in¬ 
testinal disease of parrots, and many 
other animal diseases that we cannot 
mention here. The germs of the 
parrot disease, when inhaled by man, 
produce a very severe form of pneu¬ 
monia, and the glanders germ attacks 
man and is often fatal to him. 

Diseases caused by Other Organ¬ 
isms. Many diseases of plants 
(rusts, smuts, mildews, rots, etc.) are 
caused by fungi that are related to 
the molds and mildews. These are 
much larger than bacteria, their 
bodies being composed of long, 
thread-like filaments. A few of 
these fungi attack man, a number 
of them entering the hair follicles 
and growing in the skin. Among 
the diseases caused by them are ring¬ 
worm, barber’s itch, and in tropical 
countries, an itch which attacks any part of the body. Thrush, 
which is found in the mouths of young babies, is also due to a 
fungus, and a few kinds of yeasts occasionally attack the 
human body. 

QUESTIONS 

Give some facts that show the extreme smallness of bacteria. 
Where are bacteria found? What shapes have they? 

Where does the bacillus of diphtheria grow? How long can the 
germ remain ahye outside the body ? What is the incubation period 



Fig. 151. The fungus that 
causes ringworm. 
















DISEASES CAUSED BY BACTERIA 


319 


of diphtheria? How is it contracted? How strict a quarantine is 
necessary to control diphtheria? How does diphtheria cause death? 
What is antitoxin ? Explain the antitoxin treatment for diphtheria. 
Why should the antitoxin be used in the early stages of the disease ? 

In what parts of the body does the pneumonia germ grow? How 
is the germ transferred from one person to another? Give two ways 
by which the disease may be in a measure prevented. Where does 
the grip germ grow? Why is grip a dreaded disease ? By what germs 
are catarrh and colds perhaps caused ? Why do we suppose that colds 
are germ diseases? 

Name some of the diseases caused by pus-forming germs. Of what 
is pus composed ? How should a wound made by anything clean be 
treated ? a wound made by anything unclean ? 

Where is the tetanus bacillus found? Under what conditions can 
it grow and under what conditions can it not grow? What kind of 
wounds are especially dangerous? How does the tetanus germ injure 
the body? What germ does the leprosy bacillus resemble? How is 
plague spread? 

How does the typhoid germ enter the body? What part of the 
body does it usually attack? What excretions from a typhoid 
patient contain the germs? Name some of the ways typhoid fever 
may be contracted. How does the cholera germ enter the body? 

By what germs may cerebro-spinal meningitis be caused ? Where 
do the germs grow in this disease ? In what secretion of the patient 
is the germ found? How does the germ probably enter the body? 

How may the germ that causes sore eyes be spread? Name other 
germ diseases; some germ diseases of animals ; some diseases caused 
by larger fungi. ____ 

When one has been infected with diphtheria or tetanus germs, 
antitoxin helps to keep the disease from developing. How does it 
do this? Are typhoid germs killed by freezing them in ice? 



CHAPTER XXV 


PREVENTING THE SPREAD OF DISEASE GERMS 

After most kinds of disease germs begin their growth in 
the body, medicines are of very little use except to keep up the 
body strength. In our warfare with germs, we must there¬ 
fore depend chiefly either on keeping the germs out of the 
body, or on the natural power of the body to kill them after 
they enter it. Keeping up the germicidal power of the body, 
and preventing the germs of infectious diseases from being 
scattered about, are, therefore, the most important points in 
the prevention of disease. In a former chapter (page 290) 
we have discussed the necessity of keeping up the resist¬ 
ance of the body to germs. We shall now study the best 
methods of keeping the germs that come from the bodies 
of sick persons from being spread abroad. 

DANGERS FROM INSECTS 

Fleas spread the germs of plague; mosquitoes carry many 
diseases; the house-fly is a great carrier of germs; and ticks 
and certain tropical flies are known to carry disease. 
The bedbug also is suspected of being responsible for the 
spread of certain diseases. Any insect that bites us has an 
excellent opportunity to introduce germs into the body, and 
any insect that crawls over our food, as do flies and cock¬ 
roaches, may easily spread the germs of many diseases. We 
shall do well, therefore, to guard ourselves as much as 
possible from insects. 


320 


PREVENTING THE SPREAD OF DISEASE GERMS 321 

Mosquitoes. The mosquito, more than any other one agency, 
has driven man from the warmer and more fertile portions 
of the earth to the colder and more barren regions. Not 
only does it carry the germs of malaria, but it carries yellow 
fever and dengue, or “breakbone fever,” a disease com¬ 
mon in the tropics and found to a certain extent in some 
of our Southern states. The germs of several diseases of man 
not found in our country, and of certain diseases of birds, 



FIG. 152. The life history of the mosquito. A is the malaria-carrying mosquito 
(Anopheles), and B, the common mosquito (Culex). a is the eggs; i, the wriggler; 
c, the tumbler; and d, the adult mosquito. 


are also carried by mosquitoes. Where it is possible to 
do so, the best way to end these diseases is to destroy the 
mosquitoes. To work at this intelligently it is necessary 
first to know the life history of the mosquito. 

The Life History of the Mosquito. The mosquito lays its 
eggs on water. In about a day the egg hatches into a wrig¬ 
gler that swims actively about, feeding on protozoa and other 
small animals that are in the water. The wriggler takes in 
air through a breathing tube, which it thrusts out through the 
surface of the water to the air, as shown in Figure 152. 

In from seven to fourteen days the wriggler changes its 








































322 


HUMAN PHYSIOLOGY 


form. The head and the fore part of the body become much 
heavier, and the breathing tubes shift to the back of the body. 
In this stage it is called a tumbler , because instead of wrig¬ 
gling as it swims, it tumbles over and over. In from two to 
five days-—ten to twenty days from the time the egg was 
laid — the tumbler splits down the back, and the adult 
mosquito comes out and flies away. How long a mosquito 
lives in the adult form is not known, but one has been kept 







Fig. 153. A is the malaria mosquito (Anopheles) and B is the common mosquito 
(Culex). 

for seventy-six days, and enough of them always live through 
the winter to furnish a plentiful supply for the next summer. 

Anopheles. The kind of mosquito that carries the germ 
of malaria is called Anopheles. It is a small, almost silent 
mosquito, that does most of its biting in the early part of the 
night. It can readily be distinguished from other mosquitoes 
by the black spots on its wings, and by its habit of elevating 
the back part of the body, or standing up on its head, when 
sitting and biting. The wriggler of Anopheles can be dis¬ 
tinguished from the wriggler of other mosquitoes by its 
position while breathing. The Anopheles wriggler lies 
almost parallel to the surface of the water (Fig. 152 A ), and 
the other wrigglers take a position almost perpendicular to 
t.he surface of the water (Fig. 152 B). 









PREVENTING THE SPREAD OF DISEASE GERMS 323 


Other mosquitoes are often carried considerable distances 
by the wind, but the Anopheles has a habit of clinging to 
weeds, shrubs, and bushes when the wind blows, and is 
not often found far from the place where it is hatched. The 
mosquitoes that give people malaria are usually raised by 
those same people, or by their near neighbors. 

How to destroy Mosquitoes. The first thing in the fight 
with mosquitoes is to deprive them of breeding places near 
human dwellings. An old fruit can may catch and hold 
enough rain water to breed a large number of mosquitoes; 
in the course of a summer, an almost unlimited number can 
come from a water barrel or an open cistern; and an un¬ 
drained ditch by the roadside may supply enough mos¬ 
quitoes to torment and infect with malaria all the people in 
the vicinity. 

Old cans and pans should be cleared away; water barrels, 
tanks, and cisterns should be screened so that the mosquitoes 
cannot get to them to lay their eggs; sagging eave troughs 
should be braced up so that no water will stand in them, for 
wrigglers may start here in a very small quantity of water 
and be washed down into the cistern, where they will com¬ 
plete their development. All pools and puddles about houses 
should be drained, and weeds and shrubbery in which the 
mosquitoes can find a dark, cool place to hide during the hot 
part of the day, or when the wind blows, should be cut down. 

When pools of water cannot be drained, it is an easy 
matter to kill all young mosquitoes in them by pouring a little 
kerosene on the water. This forms a film over the water, 
shutting the wrigglers off from the air, and killing them in a 
few minutes. If the kerosene is washed away by rains, it 
must be renewed within ten days, for this is about the time 
it takes a mosquito egg to grow into a mosquito. Minnows 


324 


HUMAN PHYSIOLOGY 


and tadpoles feed on the mosquito wrigglers, so by introduc¬ 
ing these into a pond, the number of mosquitoes that breed 
there may be greatly lessened. 

The work of destroying mosquitoes in cities and towns 
must be taken up by public officials who have authority 
to compel every one to put his premises in sanitary con¬ 
dition. Otherwise enough persons will keep breeding places 
for mosquitoes to infect the whole town. When the work 
is undertaken in this way, it is a simple and not at all expen¬ 
sive matter entirely to eradicate mosquitoes and malaria from 
a town, as has been done in many places. 

The Danger of Flies. There is a belief among some people 
that flies are useful scavengers. No greater mistake could 
be made, for they light in and walk over 
all manner of unclean matter, and then fly 
into the house and spread germs and un¬ 
cleanness over dishes, food, milk vessels, 
and everything that they come in contact 
with. 1 Not only do they carry germs on 
their feet, but when a fly feeds on the 
sputum of a consumptive or the wastes 
from a typhoid patient, the germs of these 
diseases are found alive in the matter from 
its alimentary canal. 

Flies may carry almost any kind of disease germs, so a 
sick person should be carefully screened away from them, and 
all matter from the body of a sick person should be destroyed 
immediately. Otherwise, every one in the vicinity is in 
danger of contracting the disease through the flies. 

1 A fly was caught and made to walk over a plate of gelatine for two minutes. 
In that time it left 289 germs in the gelatine. Another fly has been reported as 
having 100,000 germs on its legs. 



Fig. 154. The foot 
of a fly. A fly usually 
has great numbers of 
germs clinging to its 
feet. 


PREVENTING THE SPREAD OF DISEASE GERMS 325 

Keeping Free from Flies. It is possible to do much in 
the way of avoiding danger from flies by using screens and 
flypaper, by covering food and 
dishes, and by removing all 
materials that attract them to 
the house. A far easier and 
more effective way is to re¬ 
move the breeding places of 
the flies. The egg of the 
house-fly is laid in manure 
about stables, or in the matter 
in water-closets. In a day or 
less, this hatches into a small, 
white, footless maggot, which in nine or ten days from the 
time the egg was laid changes into the adult fly. 

It is estimated that in one summer 300 flies may hatch 
in a cubic inch of manure, and if the breeding places of the 
flies are left undisturbed, they will hatch faster than it is 
possible to kill them. It is a simple matter, however, to 
stop their increase by removing, once a week, all matter in 
which they breed, burying it, or spreading it on the fields 
where it will dry and the eggs and young will be killed. 

Flies can also be prevented from hatching by thorough 
sprinkling of the matter in which they breed with water con¬ 
taining a little petroleum, or by covering it with lime, or by 
keeping it covered so that the adult flies cannot get to it to 
lay the eggs. 

DANGER FROM DUST 

In a cubic yard of ordinary air, there are from a hundred 
to a thousand bacteria. These bacteria are attached to float¬ 
ing particles of matter of one kind or another. Air that 



Fig. 155. The house-fly. A is the 
egg which is laid in manure; B is the 
larva or maggot; C is the pupa or rest¬ 
ing state; and D is the adult fly. 



326 


HUMAN PHYSIOLOGY 


is absolutely free from dust is also free from bacteria, and 
by stirring up dust the number of germs in the air can be 
increased to countless multitudes. 

Germs that are not killed by drying are in dust, and on 
being inhaled may cause disease. As long as people con¬ 
tinue to spit on the streets and in other public places, the 
dust about cities and towns will contain germs of consump¬ 
tion, catarrh, and, to a certain extent, of diphtheria and pneu¬ 
monia. The dust in houses where people are sick of these 
diseases often contains the germs, and it is quite possible 
that the germs of whooping-cough, measles, mumps, and other 
contagious diseases which we do not well understand, may 
also be in dust. 

People should be prohibited from spitting where it will be 
a danger to the public, but every possible effort should also 
be made to keep down dust. Streets should be cleansed and 
sprinkled, houses should be swept with carpet sweepers or 
damp brooms, and some damp material 1 should be used in 
sweeping public schoolrooms and other public buildings. 
Schoolrooms should be swept after school so that there 
will be time for the dust to settle before the pupils assemble 
the next morning, and other public buildings should be 

1 The Michigan State Board of Health recommends the following for use in 
sweeping the floors of public buildings : 

(1) To a pailful of sawdust wet with hot or cold water, add one half pint of 
kerosene and a tablespoonful of sulpho-naphthol or formaldehyde. This ma¬ 
terial can be prepared some days in advance of its use. 

(2) Heat one third part sand, and add two thirds part sawdust. To a pailful of 
this mixture add one half pint of paraffin oil and mix thoroughly. This prepa¬ 
ration produces excellent results. 

(3) Boil one pound of salsoda and one pound of chlorid of lime in a gallon 
of water. Dampen sawdust to be used for sweeping with this solution. This 
preparation is excellent for restoring the natural color of floors. 


PREVENTING THE SPREAD OF DISEASE GERMS 32 7 

swept some time before they are to be used. Dusting 
should be done with a damp cloth that will wipe off the dust 
and take it away, for it is foolish simply to stir up the dust 
into the air, where it will be inhaled or will settle again on 
objects in the room. In rooms that are much used, hard 
floors, rugs, and plain furniture are more hygienic than heavy 
carpets and plush-covered furniture, because it is easier to 
keep them free from dust. Vacuum cleaners are recom¬ 
mended by health officials, because they remove dust and do 
not stir it up where it will be breathed into the lungs. 

DANGERS FROM WATER AND FOOD 

Typhoid, dysentery, and diarrhoea are the main diseases 
that are carried by water. All over our country, every year, 
many persons contract these diseases from the water, and 
occasionally the water supply of a city will be so infected 
that an epidemic will occur. The .way water may be pol¬ 
luted is shown by the history of the typhoid epidemic from 
which Butler, Pennsylvania, suffered in the summer and 
autumn of 1903. 

Butler was then a city of about 16,000 inhabitants, supplied 
with water from an artificial lake. A family living on the 
banks of a small stream that flowed into the lake was stricken 
with typhoid, and the wastes from the sufferers were thrown 
out on the ground near the creek. The germs found their 
way into the creek, and into the water that was used in 
the city, and soon great numbers of the inhabitants were 
stricken with typhoid, about 1200 cases developing before the 
epidemic was over. One section of the city was supplied 
with water from artesian wells, and the people using this 
water did not suffer from the disease, which shows that the 
germs were carried by the polluted water from the lake. 


328 


HUMAN PHYSIOLOGY 


Epidemics like the one in Butler are, of course, uncommon, 
but if you will investigate, you will probably find that in 
the town or community in which you live, several persons 
die each year from these water-borne diseases. 

Freeing Water from Disease Germs. By filtering through 
beds of sand, a city can take almost all dangerous germs out 
of its water supply. Many cities fail to do this, however, and 
when one must use impure city water or water from an 
ordinary well, the best plan is to boil it. Bringing it to a 
boil will kill all dangerous germs, most of them dying if the 
water is heated to 160 or 170 degrees. Most house filters are 
almost useless, for they catch matter in which the bacteria 
breed and multiply, and the bacteria pass through the pores 
in most of them. Filters made of fine porcelain do keep 
back bacteria if they are carefully cleaned and attended to, 
but this is a great deal of work, and it is easier to boil water 
than to look after a filter. It is always to be remembered 
that to wash fruits, vegetables, dishes, or milk vessels in 
impure water may be as dangerous as to drink the water. 

Disease Germs in Natural Waters. Any water that comes 
from the surface of the ground is likely to contain disease 
germs, typhoid fever being a very common disease in 
the country and in mountainous regions, where the people 
' drink from the most beautiful, clear springs. Shallow wells, 
springs, and small streams are the most dangerous of all 
waters. Cistern water, where the cistern is closely cemented 
and kept clean, is much safer. Water caught from a roof 
and stored in a tank above ground is safe, and deep arte¬ 
sian water is also free from dangerous germs. It is never 
safe to use water from a shallow well, no matter how cool 
and clear the water may be, for experience shows that people 
who use such water suffer greatly from typhoid fever and 


PREVENTING THE SPREAD OF DISEASE GERMS 329 

other intestinal diseases. Some wells are much worse than 
others, an occasional well giving typhoid to almost every 
family that uses water from it. Such a well should be filled 
up, and if water from a suspicious source must be used for 
drinking, it should be boiled. 

Keeping Bacteria out of Wells. Very few bacteria live 
deeper than three or four feet 1 in the soil. The pollution 



Fig. 156. B shows how surface water enters a well, carrying with it germs from 
the surface of the soil. A is a weil arranged to keep out surface water and germs. 
The water must not be allowed to run down behind the wall, the platform should be 
double and water tight, and water should not be allowed to run back into the well 
around the pump. 


of wells comes from surface water getting into them when 
it rains, and carrying with it bacteria from the upper layers 
of the soil. 

To keep out bacteria, a well should first of all be located 
on a high place and away from all pigpens, stables, or out¬ 
buildings that may drain into it. Around the mouth of the 

1 Where the soil is very coarse gravel or where it is underlaid by sloping, 
cracked layers of rock, germs may travel considerable distances underground. 

























330 


HUMAN PHYSIOLOGY 


well a tough clay should be spread and packed in thoroughly, 
so as to form a water-tight layer over the soil. This should 
slope so as to carry all surface water away from the well. 
A sound, clean, water-tight platform, large enough to extend 
out over the walls, should be built, so that no surface water 
whatever will run in behind the wall and get into the well. 

The whole task is to keep the surface water out of the 
well. Cementing the upper part of the well and laying a 
circle of cement over the surface of the earth above the 
mouth of the well is the surest way of doing this. Where 
there are disease germs in the ground, some of them are 
likely to get into the water, but their number can be greatly 
lessened by taking proper care of a well. Also a great deal of 
the food materials on which the germs in the water grow and 
multiply is kept out of the well by these precautions. No 
one who is nursing a case of infectious disease should come 
about the well, or at least should use great care if he does 
so, for it is an easy matter, by handling well-buckets or by 
working around a pump, to leave germs where they will 
get into the well. 

Dangers from Milk. The great danger from milk is due 
to the fact that most kinds of germs multiply rapidly in it. 
Tuberculosis is sometimes caused by milk, and the sickness 
that is so common among young children in summer is 
often due to germs in the milk. Typhoid fever, scarlet fever, 
and diphtheria may also be contracted through milk. Again 
and again it has been found that along the route of a cer¬ 
tain milkman the people were suffering from one of these 
diseases, and on investigation it would be proved that a case 
of the disease existed among those handling the milk or in 
their families; or that the bottles had been taken back from 
families where the disease was, or, in epidemics of typhoid 


PREVENTING THE SPREAD OF DISEASE GERMS 331 

fever, that the milk vessels had been washed in water from 
wells containing the typhoid germ. One article in a medical 
journal reported 330 epidemics traceable to milk, of which 195 
were typhoid epidemics, 99 were epidemics of scarlet fever, 
and 36 were diphtheria epidemics. It is difficult for a private 
citizen to guard himself against these dangers, and in all well- 
governed cities and towns a health officer looks after the 
milk supply. 

Keeping Milk Free from Germs. All milk vessels and feed¬ 
ing bottles for babies should be thoroughly scalded every day 
to kill the germs in the milk that adheres to them. Other¬ 
wise these germs will multiply in the new milk, and soon 
it will be filled with them (page 303). Milk vessels should 
never be rinsed in any but boiled water, the purest of rain 
water, or artesian water, for one dangerous germ that gets 
into the milk from the water remaining on the vessels may 
grow into a multitude. Milking should be done in a clean 
building that has fly screens on it, and everything possible 
should be done to keep dust and hairs out of the milk, for 
these are swarming with germs. The milk should be cooled 
as quickly as possible, and kept cool to prevent the germs 
from multiplying so rapidly (page 130). It should be used 
before it becomes old, for milk that at first has only a mod¬ 
erate number of germs in it may soon be filled with countless 
myriads of them. It is also necessary for a medical officer 
to examine the cows from which the milk comes, or there 
will frequently be living tuberculosis germs in the milk 
(page 341). 

Killing Germs in Milk. When it is impossible to obtain 
clean fresh milk, it is often advisable to heat milk to 170 
degrees or a little higher for a few minutes, or to heat it to 
155 degrees for half an hour. This destroys most of the 


332 


HUMAN PHYSIOLOGY 


germs in the milk, and a person using the milk has fewer of 
them to kill out. A few children, however, do not digest the 
heated milk so well as raw milk, and heating does not render 
wholesome very old milk, in which the germs already have 
produced large quantities of toxins and acids. In the sum¬ 
mer, however, ordinary milk is in most cases greatly im¬ 
proved by heating. 

Dangers from Other Foods. Almost any food may be a 
carrier of disease if it has been exposed to flies or placed 
where dust may blow on it. The intelligent citizen buys his 
food from the groceryman who keeps a clean store and 
screens his fruits and vegetables from flies. 


DISINFECTION 

It cannot be too strongly emphasized that nearly all 
our germ diseases come from other persons who are diseased, 
and that insects, dust, water, and milk are sources of danger 
because they may become contaminated with germs from the 
body of some person. In preventing the spread of germ dis¬ 
eases, the destruction of the germs in sputum and in the 
other discharges from the bodies of the sick is therefore more 
important than any other precaution. It is well for every 
one to know some of the ways of killing germs. 

Drying. Many germs, especially germs like the typhoid 
and cholera germs, die if they are thoroughly dried. No 
disease germs can grow and multiply when dry, and suffi¬ 
cient drying will kill almost any germ. Yet the tuberculosis 
germ can stand weeks and months of drying, and the germ 
of tetanus may be dried almost indefinitely without killing it. 
Therefore it is usually not safe to depend on drying alone 
to disinfect anything; but a damp house keeps alive the 


PREVENTING THE SPREAD OF DISEASE GERMS 333 


germs that are in it, and consumption, pneumonia, and other 
diseases are more likely to develop in a damp house than in 
a dry house. 

Light. Light is injurious to bacteria, bright sunlight kill¬ 
ing many germs in a few hours, and a moderately strong 
light assisting in checking their growth. It is an excellent 
practice to expose bedclothes and rugs to the sun, and to 
throw up the shades and allow the light to enter houses. In 
rooms occupied by consumptives, or by pneumonia, diph¬ 
theria, or grip patients, this is especially valuable. Besides 
the effect which light itself has on the bacteria, admitting the 
light dries out a room, and assists in this way in killing the 
germs. Dirt and dust, mingled with sweat and oil from 
the skin, on doorknobs, banisters, and furniture, protect 
germs from light and drying, thus keeping them alive. For 
this reason the doorknobs and desks in schoolrooms should 
be cleaned occasionally with soap and hot water. 

Heat. Boiling water kills the germs of all common dis¬ 
eases, and handkerchiefs, dishes, and clothing that have be¬ 
come infected can be made safe again by thoroughly boiling 
them. Articles of little value, and sputum from patients 
sick of respiratory diseases, may often be most conveniently 
disposed of by burning (page 342). The surfaces of dishes 
contain tiny crevices in which germs lodge, and in disin¬ 
fecting dishes with hot water, it is necessary to leave them 
for a few minutes in boiling water, so that the heat will reach 
the germs in the crevices. 

Chemical Disinfection. Certain chemicals are so poison¬ 
ous to germs that they are extensively used in disinfecting. 
A physician should always be consulted as to which disin¬ 
fectant is best for a particular purpose, and exactly how to 
use it, for some of them are better for one purpose than 


334 


HUMAN PHYSIOLOGY 


for another. Since most of these disinfectants are very poi¬ 
sonous, an excellent plan is to add a little red ink or other 
coloring matter to them so that they will not be mistaken 
for water. The following are some of the most commonly 
used disinfectants : 

Bichlorid of mercury (corrosive sublimate) dissolved in 
water, with one part of the bichlorid to a thousand parts of 
water (i dram to I gallon of water), kills nearly all kinds of 
germs in two or three minutes, and all kinds in fifteen min¬ 
utes. This can be purchased in tablets of the right size to 
make a pint or half pint of the disinfectant of the proper 
strength. It is convenient, and an excellent disinfectant for 
the hands, for washing floors and furniture, and for disinfect¬ 
ing clothing that can be soaked in it. It cannot be used on 
metal, as it destroys it, and is not good for disinfecting where 
there is much organic matter present, as there is in dis¬ 
charges from persons sick with typhoid and other intestinal 
diseases. 

Bimodid of mercury is more than twice as powerful as 
bichlorid of mercury, and need be made only half as strong. 
It is one of the best general disinfectants, and is especially 
useful in disinfecting the hands, since it does not injure the 
skin as do most other disinfectants. 

Carbolic acid\ made up in a 2J per cent solution (3-|- ounces 
of liquid carbolic acid to 1 gallon of water), is as strong as 
the bichlorid of mercury solution described above. This is a 
very reliable disinfectant, good for almost any purpose. For 
disinfecting sputum and other discharges from the body it is 
well to use a 5 per cent solution. 

Lysol is about the same strength as carbolic acid. It often 
destroys the colors in clothing. 

formalin is about one half as strong as carbolic acid, a 5 


PREVENTING THE SPREAD OF DISEASE GERMS 335 

per cent solution being equal to a 1 to 1000 solution of 
bichlorid of mercury. It loses its strength if exposed to the 
air. By heating formalin, a gas called formaldehyde is driven 
off. This is the best of all gaseous disinfectants. 

Chlorid of lime , made by adding ounces of chlorid of lime 

to 1 gallon of water, is a cheap and powerful disinfectant. 

Milk of lime is a powerful disinfectant It is made by 
adding one part of freshly slaked lime by weight to four 
parts of water. This is a cheap disinfectant, and, for certain 
purposes, is as effective as anything that can be employed. 
It should not be used in sinks, for it will cause trouble with 
the traps. Air-slaked lime is worthless. 

Special Points in disinfecting. Any one who is waiting on a 
person sick with an infectious disease should frequently and 
thoroughly disinfect his hands, holding them for several 
minutes in the disinfectant. Washing the hands thoroughly 
with soap assists very greatly in freeing them from germs. 
Keeping the nails trimmed and the skin smooth makes the 
hands easier to disinfect. 

For treating an infected wound or a sore, peroxid of hydro¬ 
gen and iodin are often used. A weak solution of carbolic 
acid or a carbolic salve is also good, and washing with warm 
v salt water is useful (page 312). In vaccination the skin 
should be cleansed, clean instruments used, and the wound 
protected; for the greatly swollen arms and running sores 
that sometimes follow vaccination are caused by pus-forming 
germs that get into the wound. 

Irf typhoid fever, the germs are in the discharges from the 
bowels and the kidneys, and should be received in vessels 
containing disinfectants. Strong limewater is excellent for 
this, and carbolic acid is also good. It is necessary to see 
that the disinfectant is thoroughly mixed with the waste 


336 


HUMAIV PHYSIOLOGY 


matter, and it should be allowed to stand for several hours to 
make sure that all germs are killed. 

In diphtheria, pneumonia, consumption, grip, measles, 
scarlet fever, and spinal meningitis, the germs are in the dis¬ 
charges from the throat and nose. It is best to receive these 
discharges in strong disinfectants, carbolic acid being good 
for this purpose. Above all, do not allow the discharges to 
dry and become scattered about. All handkerchiefs, dishes, 
and other infected articles should be placed at once in boiling 
water or soaked in carbolic acid or bichlorid of mercury. 
These substances are poisonous, and must afterwards be 
rinsed off dishes. Additional instructions in regard to the 
disinfection of sputum will be found in the chapter on con¬ 
sumption (page 342). 

Where a whole room or house is to be disinfected, it is 
usually done by fumigating. Formaldehyde, or sometimes 
sulphur, is used for this purpose. Special directions are 
necessary for this work if it is to be effectively done. Quick¬ 
lime is a good disinfectant for cellars and closets, and the 
germs in any matter that is buried in quicklime will be 
killed. 

Mistaken Ideas in Regard to Disinfection. The idea that 
there is some connection between the smell of a substance 
and its power as a germ killer is prevalent. Odoriferous 
substances are sometimes burned in rooms containing sick 
persons, or a little carbolic acid exposed in a saucer so that 
it will scent the air of the room. It need hardly be pointed 
out that germs are not injured by anything of this kind. 

Unhygienic Habits. There are numerous ways by which 
germs can get into the body, and we will call attention to 
a few habits which give them a special opportunity to do 
so. One of these is the habit of putting pencils and other 


PREVENTING THE SPREAD OF DISEASE GERMS 337 

objects into the mouth, often after these same objects have 
been in the mouths of other people. Another is the habit 
of drinking from the same cup that others use. Germs may 
easily be left on a cup by any one who has them in his mouth, 
and each child in school should have his own cup, and in 
traveling one should carry a private cup. When it is neces¬ 
sary to drink from a public cup, it is better to put both lips 
into the cup and drink without taking the edge of ,the cup 
into the mouth. One other habit that we would mention is 
that of allowing the fingers to touch the face, eyes, or lips. 
In many ways — from books, doorknobs, pencils, seats and 
straps in street cars, and from the hands of other persons — 
we get germs on our hands. It is, therefore, advisable to 
form the habit of keeping the hands away from the face. 
Especial attention should be given to this point when sore 
eyes are prevalent. A good habit to form is that of washing 
the hands with soap before eating (page 335)* 

Freeing the Country Farmhouse from Disease. By intel¬ 
ligent effort, families living in the country can greatly de¬ 
crease the risk of exposure to germs. If they will clear 
away weeds and dense shrubbery from around their homes 
and look after the breeding places of mosquitoes, they can do 
much to protect themselves against malaria. By removing 
the breeding places of flies and guarding their own milk and 
water supplies, they can in a great measure free themselves 
from typhoid fever. Sunlight admitted to the house is a 
great aid in keeping the atmosphere free from germs, and 
the fresh country air admitted freely to the sleeping rooms 
at night will do much to build up the body and increase its 
germicidal power. Germ diseases are almost as prevalent in 
the country as in the city, but with a little care a family in 
the country can, to a great extent, avoid them. 


338 


HUMAN PHYSIOLOGY 


City and Village Improvement. If the inhabitants of cities 
and towns will work together, they can do much that will give 
them more healthful and also more pleasant and beautiful 
places to live. Sprinkling the streets and sodding with grass 
along the sidewalks will help to keep down the dust. Clean 
sidewalks are pleasanter than sidewalks that are covered 
with sputum, and a street car that has been soiled by persons 
spitting on the floor is neither inviting nor sanitary. By 
cutting down the weeds and looking after the breeding 
places of mosquitoes, the town is made more beautiful and 
attractive as well as freed from malaria, and killing out the 
flies saves us from annoyance as well as from disease. The in¬ 
telligent citizen favors the improvement of his town because 
it gives him a more pleasant place to live, and because he 
knows that it costs far less to make a town clean and health¬ 
ful than to have all the disease that comes from insects, 
unclean streets and sidewalks, dust, bad water, and impure 
milk. 

The Necessity for Public Health Officials. There are 
always some careless persons who will spread disease if 
they are permitted to do so, and in a town or city, it is 
impossible for a person to protect himself against germ 
diseases by his private efforts. He has no control of his 
neighbor’s flies and mosquitoes, and he cannot prevent con¬ 
sumptives from scattering germs about where he is likely 
to inhale them. If he lives in a city, he has no water ex¬ 
cept that which comes to him through the city water mains, 
and no milk supply except that which the milkman furnishes 
him. His children may go to school and there be kept in 
an unclean, badly ventilated schoolroom, and seated beside 
some one who has just recovered from diphtheria, and who 
is still carrying virulent diphtheria germs in his throat. With- 


PREVENTING THE SPREAD OF DISEASE GERMS 339 


out public health officers, a private citizen will be exposed 
in a hundred ways to danger from disease germs. It is, 
therefore, the duty of every good citizen to uphold the 
health officials and to work with them, and every one should 
realize that it is a great moral crime to scatter abroad 
germs that may cause sickness and death. 

Summary. Disease germs are carried by insects, dust, 
water, and food, and in other ways. They come from per¬ 
sons who have germ diseases. By destroying the germs that 
come from these persons, more can be done to prevent sick¬ 
ness than in any other way. Cbuntry people may protect 
themselves against germs, but in cities and towns health 
officials are necessary. 

QUESTIONS 

What insects carry disease germs? What diseases are carried by 
mosquitoes? Give the life history of the mosquito. How may the 
malaria-carrying mosquito be distinguished from other mosquitoes? 
How may mosquitoes be destroyed? How do flies carry germs? 
How may flies be destroyed ? Mention some measures that assist 
in the prevention of dust. 

Name some diseases that are carried by water. Tell of the 
Butler typhoid epidemic. How may water be kept safe from 
germs? What natural waters contain disease germs? What kinds 
are safe? Tell how to protect a well from germs. What diseases are 
carried by milk? What measures are necessary to keep milk safe 
from germs? How may disease germs in milk be killed? What 
precautions should be taken to keep germs from foods? 

Name four ways in which germs may be killed. Name some 
common chemical disinfectants. How should sputum be disposed 
of ? Mention some unhygienic habits. What measures will assist 
in freeing a farmhouse from disease? in freeing cities and towns 
from disease? Why are health officials necessary? 


CHAPTER XXVI 


TUBERCULOSIS 

About one seventh of the human race and one tenth of the 
inhabitants of the United States die of tuberculosis. Each 
year this disease claims in Europe about one million vic¬ 
tims, and in our own country about one hundred and fifty 
thousand. This means that each day four hundred of our 
countrymen die of tuberculosis, and that eight millions of 
the people now living in the United States will die of the dis¬ 
ease. It is estimated that tuberculosis costs our nation in 
money $330,000,000 a year, an annual sum that, if properly 
expended, would free the land from the disease. 

The Bacillus of Tuberculosis. Tuberculosis is caused by a 
slender bacillus that attacks most vertebrate animals as well 
as man. It may grow in almost any part of 
the body and cause tuberculosis of the part 
affected. When it grows in the intestine, it 
causes tuberculosis of the intestine. When it 
grows in the bone, it causes tuberculosis of 
the bone. When it grows in the lymphatic 
glands, it causes the disease formerly known 
as scrofula, and when it grows in the lungs, 
it causes tuberculosis of the lungs, or con¬ 
sumption. The germ of tuberculosis may also grow in the 
skin, kidneys, liver, or larynx, but it most frequently attacks 
the lungs. 



Fig. 157. The 
bacillus of tuber¬ 
culosis. 


340 



TUBERCULOSIS 


341 


The bacillus of tuberculosis is slow-growing, but it is so 
hardy that it often resists all efforts of the body to kill it, and 
grows steadily on and on until it causes death. Outside of 
the bodies of men and animals, it does not grow at all in 
nature, and under the influence of light and drying, it finally 
dies. Yet in the sputum of a consumptive, it often lives for 
two or three months — sometimes for one or two years. Dried 
sputum blowing about in dust is therefore a very great source 
of danger to all who breathe it in. Away from the habitations 
of men and animals, the tuberculosis germ is not found, but 
it is frequently present in the dust of rooms that have been 
occupied by careless consumptives. 

HOW TUBERCULOSIS IS CONTRACTED 

Tuberculosis is contracted from men and animals that have 
the disease. The germ gets into the body usually either from 
the milk of diseased cattle or, more commonly, from the 
sputum of a consumptive. 

Tuberculosis Germs in Milk. A great number of cattle are 
affected with tuberculosis. Occasionally the germs are in 
meat, but more frequently they are in milk. 1 It is known 
that the germs of tuberculosis can pass through the wall of 
the alimentary canal, be carried by the blood to the lungs, 
and there start consumption. Since no one wants to drink 
living tuberculosis germs in his milk, dairy cattle should 
certainly be properly inspected to see that they are free from 
this disease. Yet the Alaska Indians, the Filipinos, and 
many other peoples who do not use milk suffer greatly from 

1 From examinations of milk made in Washington, D.C., it was estimated 
that almost 7 per cent of the milk sold in the city contained living tuberculosis 
germs. The germs are also found in butter that is made from infected milk, and 
will remain alive and virulent in butter for weeks and months. 


342 


HUMAN PHYSIOLOGY 


tuberculosis, and it is probable that most tuberculosis comes 
not from milk, but from persons who have consumption. 

Dangers from Sputum. In the advanced stages of con¬ 
sumption, the sputum that is brought up from the lungs 
each day contains several billion germs. This sputum 
should never be swallowed, for if this is done, there is danger 
that the disease will be started in the walls of the alimentary 
canal, or that the germs will get into the blood and be carried 
to parts of the body that have not yet been infected. It is 
also unsafe to spit the sputum out where it will be exposed 
to flies, or to let it dry and blow about, for it may cause 
other people to contract the disease. The germs in the 
sputum should therefore be destroyed. 

Disposal of Sputum. The sputum from a consumptive 
should be received in a vessel that contains a disinfectant 
(carbolic acid or chlorid of lime is good for this purpose), or 
in pasteboard cups that may be burned. Sometimes the 
sputum is received in vessels that contain water, and is then 
disinfected with boiling water or buried in lime, but it is 
safer to receive it in a disinfectant. When the consumptive 
is away from home, he may use pieces of cloth and seal them 
up in waterproof envelopes that are made for the purpose, 
until they can be destroyed. 

Other Precautions to be taken. A consumptive should 
always hold a handkerchief before his face when he coughs, 
and these handkerchiefs should be placed in disinfectants, or 
should be thoroughly boiled. He should learn to keep his 
hands away from his face and mouth, and should occasionally 
wash his hands in a disinfectant. He should have his own 
dishes, and these should never be washed with those of the 
family, nor allowed to come in contact with them until they 
have been boiled for at least five minutes. His bedclothes, 


TUBERCULOSIS 


343 


clothing, and furniture ought occasionally to be disinfected, 
or at least exposed to the bright sunshine as much as possible, 
and his clothing should be boiled before it is washed with 
other clothes. A consumptive should have a sleeping room 
to himself, and this room should be kept bright and well 
ventilated, to help kill any germs that may be free in it. 
A house in which a consumptive has lived should be dis¬ 
infected before any one else moves into it. 

Danger from a Consumptive. If care be taken, a consump¬ 
tive can live with his family with little danger to them ; but 
if he is careless and scatters about the millions of germs 
that come from his lungs, he is a real source of danger to all 
who come in contact with him. Many persons have a great 
fear of all consumptives, but this is unreasonable, for it is 
only the careless consumptive that is to be feared. 

THE TREATMENT OF CONSUMPTION 

Probably every one inhales tuberculosis germs at some 
time, and in the lungs of most persons there are scars show¬ 
ing where the tubercle bacilli have started to grow, but have 
been destroyed. It is, therefore, a great mistake to think 
that consumption is incurable. 

Importance of Early Treatment. Any one who has symp¬ 
toms of consumption 1 should not try to persuade himself 
that his symptoms have no existence, for this will not stop 
the growth of the germs. He should not lose valuable time 
experimenting with patent medicines, for there is no medi- 

1 The most common symptoms of consumption are cough, loss of appetite, 
gradual loss of flesh and strength, fever, night-sweats, and blood-spitting. The 
cough is often absent in the early stages of the disease. Only an examination by 
a reliable physician should satisfy one. 


344 


HUMAN PHYSIOLOGY 


cine known that will cure consumption. The only sensible 
thing for him to do is to be examined at once by a physician 
who thoroughly understands the disease. Then, if he finds 
that the germs have gained a foothold in his lungs, he should 
give himself the best possible treatment at once, for every¬ 
thing depends on starting the treatment early. 

Important Factors in Treatment. In the successful treatment 
of consumption, the following are the more important factors : 

Rest. If a consumptive can be kept quiet, much of the 
toxin that is produced by the germs will be thrown off in the 
sputum. Anything that causes the breathing to be quick¬ 
ened and deepened causes more of the toxin to be carried 
from the lungs through the body, and increases the fever. 

A consumptive should therefore have rest. If he has 
fever, he should have absolute rest, not even walking about 
his room. Laughing and loud talking should be avoided, 
and coughing should be refrained from as much as possible. 
When there is no fever, a little exercise may be taken, but it 
should be taken with care. 

Food. A consumptive should have an abundance of food, 
especially of proteid and fatty foods. Meats, eggs, milk, 
and any other good foods that he can eat and digest should 
be taken. Lunches should be eaten between meals and on 
retiring. The foods must be well prepared and served in 
different ways, or the patient will become tired of them. 

Outdoor Life. Nothing in the treatment of consumption is 
more important than fresh air, and the disease has been most 
successfully treated where the patients have lived and slept 
in the open air, summer and winter. Usually an upper porch 
can be arranged with little expense, so that the patient can 
sleep on it. In outdoor sleeping in winter, it is necessary to 
have warm clothing and to wear some kind of hood to protect 


TUBERCULOSIS 


345 

the head and neck, and in many places in summer it is neces¬ 
sary that the patient be screened from mosquitoes. 

Other Important Points. Warm and dry clothing is of 
course important, and if a consumptive lives indoors, he 
should, above all else, be sure to have plenty of fresh air. 
Consumption is much more frequent in damp houses and on 
wet soils, than it is in dry houses and on sandy soils. A con¬ 
sumptive should not remain in a damp house, and if he lives 
outdoors, he should locate himself on a dry soil. He should 
not worry about his disease being inherited, but should be 
cheerful and hopeful, 1 for if he takes his disease in time, he 
has every reason to hope for recovery. 

Sanatoria for Consumptives. Many states have established 
sanatoria to which consumptives can go, and, at a slight ex¬ 
pense, remain until they recover from the disease. 2 This is 
sensible, for in a sanatorium a consumptive can have proper 
food and care at much less expense than he can have them 
at home, and the physicians in the sanatorium know how to 
disinfect so that there is no danger of the spread of the 
disease. It is much more economical for the people of a 
state to care for their consumptives in sanatoria than out of 
them, and it is much pleasanter both for the consumptives 
and for those who have not the disease. 


1 When consumption carries away several members .of a family, the trouble is 
not so much that the disease is inherited (page 289), as that the members of 
the family contract the disease from each other. It has been found that persons 
who have married consumptives, or who have lived in houses that were infected 
with the germ, contract the disease almost as frequently as do the children or 
the brothers and sisters of consumptives. 

2 Many state and city boards of health publish circulars giving very full and 
detailed information in regard to the treatment of consumption. A consumptive 
should write to the health board of his state for these circulars, for they will 
enable him to care for himself much more intelligently. 


346 


HUMAN- PHYSIOLOGY 


The Effect of Climate on Consumption. It was formerly 
supposed that climate was very important in the treatment 
of consumption, but consumptives are now being cured in 
all our states, and it has been found in treating this disease, 
that rest, food, and fresh air are of much more importance 
than climate. Unless a consumptive has money enough to 
support himself without work and to give himself proper 
care, he should not leave his home for a distant state. For 
in many places consumptives are not welcomed, and it is 
better to be at home and have the proper care than to be 
without money or friends in the best climate in the world. 
A hot climate or a high elevation, however, is injurious to con¬ 
sumptives, for in such a place the respiration is quickened. 

Summary. Tuberculosis costs us 150,000 citizens and 
$330,000,000 annually. It is sometimes contracted from 
milk, but usually from the sputum of consumptives. Con¬ 
sumption readily yields to treatment when taken in the early 
stages. Rest, an abundance of food, and fresh air are the 
most important factors in the successful treatment of the 
disease. 

QUESTIONS 

Give some facts that show the importance of tuberculosis. Tell 
something about the bacillus of tuberculosis. How does it get into 
the body? How do tuberculosis germs that are swallowed in milk 
get to the lungs ? Why is there reason to think that sputum is a 
more common cause of consumption than milk? Why should sputum 
be destroyed? How may this be done? What other precautions 
should be taken in consumption? When is a consumptive to be 
feared? Give three important factors in the treatment of consump¬ 
tion. Mention some other points that are to be looked after. What 
advantages come from having sanatoria for consumptives? How 
important is climate in the treatment of consumption ? 


APPENDIX 


A. FOODS 

When the foods are oxidized in the cells, and when a piece of 
wood is burned in the fire, the process is the same, — the molecules 
are broken down, and their atoms are united with oxygen. What 
happens to the foods within the cells may perhaps be made clearer, 
therefore, by considering what happens in the burning of a piece of 
wood or coal in a fire. 

The Burning of a Piece of Wood. Lay a piece of wood in the fire, 
and in a little while the wood is all gone. A few ashes may remain, 
but these are only a little mineral matter that was in the wood and 
did not burn. What has become of the wood? 

The answer is that the wood has been changed to gases 1 which 
you cannot see, and has passed off into the air. The wood mole¬ 
cules, like starch and sugar molecules, are built up of atoms of car¬ 
bon, hydrogen, and oxygen. In the fire these large molecules are 
broken to pieces, and the atoms in them unite with the oxygen of 
the air. The carbon, when it unites with oxygen, forms carbon 
dioxid. The hydrogen of the wood goes off in water vapor, which 
is invisible when it is hot. By holding a cold 2 glass vessel over a 
burning piece of wood or over a burning candle, you can catch and 
condense on the inside of the vessel the water that is given off. 
Of what elements is the fat of a candle composed? (Page 83.) 
Is the water in the candle, or is it formed when the fat burns? 

1 Smoke is composed of fine pieces of carbon that fly off into the air with¬ 
out being burned. Only a very small part of wood or coal passes off in this way. 

2 The vessel must be held over the flame only a very short time, or it will 
become so, hot that the water will not condense on the glass. A tall vessel made 
of heavy glass should be used. 


347 


348 


APPENDIX 


Energy set Free by Oxidation. Energy is stored in wood molecules* 
and in the fire we get heat and light from these molecules; energy is 
stored in the molecules of coal, and an engine gets its heat and its power 
to move from burning coal; in the food molecules, too, energy is stored, 
and by burning these molecules the cell gets its heat and its power to 
work. By oxidation, the energy in the molecules is set free. 

Amount of Energy needed by the Body. A man doing light work 
needs daily food sufficient to furnish 2500 Calories} If he does 
moderately heavy work, he needs food enough to furnish 3000 
Calories; and if he does heavy work, he needs food enough to give 
3500 to 4000 Calories. Many hard-working men eat food sufficient 
to give 5000 Calories, and some lumbermen working in the Maine 
woods in the cold of winter were found to be eating enough food 
daily to furnish 8000 Calories of heat. It will thus be seen that the 
amount of energy the body needs depends very largely on the 
amount of work done, and on whether the body is exposed to cold. 

Amount of Food needed. It is generally supposed that from one 
hundred to one hundred and twenty-five grams (about four ounces) of 
dry proteid matter a day is needed to keep the body in the best of 
health (page 124). In nearly every community, however, there is 
some person who eats chiefly fruits, nuts, or vegetables, and gets far 
less than this amount of proteid, and the working classes of the Jap¬ 
anese live on about forty-five grams of proteid a day. Also, at Yale 
University, Professor Chittenden has conducted experiments on 
teachers, soldiers, and university athletes. For five months these 
men lived on from forty to sixty grams of proteid matter a day,— 
about one third to one half of the amount generally supposed to be 

1 A Calorie is the amount of heat required to raise the temperature of one liter 
of water i°C. Not all the energy of the foods is used in warming the body, part 
of it being used in building protoplasm, enzymes, and other substances, and 
part of it by the muscles in d( mg work. But the easiest way of measuring the 
amount of energy in food is to try how much heat it will give off when it is 
burned. The amount of energy in food, therefore, is always given in Calories, 
or the amount of heat which it yields when burned. 


APPENDIX 


349 


necessary to keep a man in health. They all kept in good health, 
and most of them gained in weight. The teachers were able to do 
good mental work, and some of them thought that their minds were 
clearer than ever before. The soldiers attended to their drills and 
exercises without trouble. The athletes gained decidedly in strength ; 
they were victors in many contests, and one of them won the Colle¬ 
giate and All-around Intercollegiate Championship of America in 
Athletics while living on this small amount of proteid. It therefore 
appears that some persons at least can live on far less than one hun¬ 
dred grams of proteid a day. In the opinion of most physiologists, 
however, it is better for most of us to take a larger amount. 

Besides the necessary amount of proteid, we must have food to 
furnish energy. We have already seen that the amount of food we 
need for this purpose varies, and that it is best to take for energy 
foods, carbohydrates and fats (page 124). The exact proportions of 
the fats and carbohydrates are not important. The following is an 
old diet for a man doing moderate work, in which the different foods 
are probably in about the right proportions : — 

Proteids Fats Carbohydrates Calories 

118 gms. 56 gms. 500 gms. 3055 

•QUESTIONS AND PROBLEMS 

1 gram proteid — 4.1 Calories. 1 kilogram — 2.2 pounds. 

1 gram carbohydrate = 4.1 Calories . 1 pound = 453*6 grams. 

1 gram fat — 9.3 Calories. 1 ounce — 28.3 grams. 

To walk 1 mile on the level requires for a man of average weight (154 
pounds ) energy equal to 59 Calories. 

To ascend 100 feet (as in climbing a hill or a flight of steps') requires 
energy equal to 15.4 Calories. 

Which is the cheaper food, cabbage or candy? tomatoes or peanuts? 
bananas or raisins ? 

How far could a man walk on the energy in 10 cents’ worth of tenderloin 
steak? on the energy in 10 cents’ worth of rice? on the energy in 10 
cents’ worth of sugar ? 


350 


APPENDIX 


Name of Food 

Price per 
Pound 

Inedible 

Portion 

Edible Portion 

Per Cent of Available 
Proteid Fat and Car¬ 
bohydrate in Food 
as Purchased 

Water 

Unavailable 

nutrients 

Available nutrients 

Proteid 

Eli 

Carbo¬ 

hydrates 

Min¬ 

erals 

Proteid 

Oj 

Eli 

Carbo¬ 

hydrate 


f 

% 

% 

% 

% 

% 

% 

% 

% 

% 

% 

Apples . . . 

x -5 

25 

84.6 

1.6 

•3 

•5 

12.8 

.2 

.225 

•375 

9.6 

Bananas . . . 

7 

35 

75-3 

2.7 

1 

•5 

19.9 

.6 

•65 

•325 

12.9 

Beans (dried) . 

5 


12.6 

7-5 

15.8 

1.6 

59-9 

2.6 

15.8 

1.6 

59-9 

Beef (round) . 

14 

7.2 

65-5 

1.6 

i9-7 

12.9 

— 

.8 

18.2 

11.9 

— 

Beef 1 . . . . 

25 

I 3-3 

60.6 

1.8 

17.9 

19.2 

— 

.8 

x 5-5 

16.6 

— 

Bread (white) . 

5 


35-3 

3-3 

7- x 

1.2 

5 2 -3 

.8 

7- x 

1.2 

52.3 

Bread (graham) 

5 

— 

35-7 

3-4 

6.9 

1.6 

5 x -3 

1.1 

6.9 

1.6 

5 x -3 

Breakfast food 2 

7-5 

— 

9.6 

4-5 

9-3 

1.6 

74 

1 

9-3 

1.6 

74 

Butter . . . 

25 

— 

11 

4.9 

1 

80.8 

— 

2-3 

1 

80.8 

— 

Cabbage . . . 

2-5 

iS 

9i-5 

•7 

1.2 

•3 

5-5 

.8 

1 

•25 

4-675 

Candy . . . 

20 

—■ 

— 

4 

— 

— 

95 

1 

— 

— 

95 

Cheese . . . 

16 

— 

34-2 

3-4 

25.1 

32 

2.4 

2.9 

25.1 

32 

2.4 

Corn meal . . 

2 

— 

12.5 

4 

7-5 

i-7 

73-5 

.8 

7-5 

x -7 

73-5 

Corn (canned) . 

5 

— 

76.1 

i-7 

2.1 

1.1 

18.3 

•7 

2.1 

1.1 

18.3 

Eggs (boiled) . 

14 

11.2 

73-2 

1.2 

12.8 

11.4 

— 

.6 

xx -3 

10 

— 

Filberts . . 

20 

52 

3-7 

10.7 

x 3-3 

58.8 

11.7 

1.8 

6.3 

28.2 

5-6 

Fish 3 . . . . 

10 

54-8 

76.7 

1 

20 

1.6 

— 

•9 

9 

.72 

— 

Fish (salt cod) . 

7 

24.9 

53-5 

6.8 

20.9 

•3 

.— 

18.5 

x 5-7 

.22 

— 

Fowl 4 . . . . 

IS 

25-9 

63-7 

1.6 

18.7 

x 5-5 

— 

.8 

13.8 

11.48 

— 

Liver .... 

IS 

7 

71.2 

1.2 

20.4 

4-3 

x -7 

1.2 

18.97 

4 

1.58 

Milk (whole) 

3 


87 

•5 

3-2 

3-8 

5 

•5 

3-2 

3-8 

5 

Milk (skimmed) 

1 

— 

9°-5 

•3 

3-3 

•3 

5- 1 

<5 

3-3 

•3 

5- x 

Mutton (loin) . 

20 

16 

50.2 

2.4 

x 5-5 

3 x -4 

— 

.6 

x 3 

26.3 

— 

Oatmeal (dry) . 

4 

— 

7.8 

5-6 

i3-4 

6.6 

65.2 

1.4 

x 3-4 

6.6 

65.2 

Oysters (solid) . 

30 

— 

88.3 

.6 

5-8 

1.2 

3-3 

.8 

5-8 

1.2 

3-3 

Peanuts . . . 

10 

25 

9.2 

10.7 

21.9 

34-7 

22 

x -5 

16.4 

26 

16.5 

Peas (green) 

7 

45 

74.6 

2.2 

5-2 

•5 

16.7 

.8 

2.86 

•275 

9.18 

Pork (fresh loin) 

12 

19-7 

5-2 

2.2 

16.1 

28.6 

— 

.8 

12.9 

22.96 

— 

Pork (salt ham) 

20 

13.6 

40.3 

3-6 

15.8 

36-9 

— 

3-6 

13.6 

31.88 

— 

Potatoes (white) 

i-5 

20 

78.3 

1.4 

i-7 

.1 

17.7 

.8 

1.36 

.08 

14.16 

Potatoes (sweet) 

2 

20 

69 

2.1 

i-3 

.6 

26.2 

.8 

1.04 

.48 

20.9 

Prunes (dried) . 

10 

15 

22.3 

8-3 

1.6 

— 

66.1 

x -7 

1.36 

— 

56.1 

Raisins (dried) . 

10 

10 

14.6 

9- x 

2 

. 3 

68.7 

2.6 

1.8 

2.7 

61.8 

Rice .... 

8 

— 

12.3 

'3-7 

6-5 

•3 

76.9 

•3 

6-5 

•3 

76.9 

Strawberries 

7 

5 

90.4 

1 

.8 

•5 

6.8 

•5 

.76 

•475 

6.46 

Sugar .... 

6 

— 

— 

— 

— 

— 1 

100 

— 

— 

— 

100 

Tomatoes . . 

1 

— 

94-3 

•4 

•7 

•4 

3-8 

•4 

•7 

•4 

3-8 

Watermelon . 

1 

60 

92.4 

•9 

•3 

.2 

6 

.2 

.12 

.08 

2.4 


* (tenderloin.) a (wheat.) 3 (black bass, whole.) 4 (chicken, feathers removed.) 





























APPENDIX 


351 


Fuel Values 
of Food as 
Purchased 

Cost of 
Proteid 

Cost of ioo Cal¬ 

ories of Heat 



Amount 

for Ten Cents 


Ounces 

Grams 

Number of 

Calories 

Per 

pound 

Per 100 
grams 

Per 

pound 

Per 100 
grams 

Proteid 

4 -» 

Cj 

in 

Carbo¬ 

hydrate 

Proteid 

a 

in 

Carbo¬ 

hydrate 

Cals. 

Cals. 

Dols. 

Dols. 









198 

43 

6.66$ 

1.47 

•75 

.24 

•4 

10.2 

6.8 

11 -3 

290.3 

1320 

265 

58 

10.76 

2-37 

2.64 

.14 

.07 

2.9 

4-2 

2.1 

83.6 

378 

1475 

3 2 5 

• 3 1 

.068 

•34 

5-°5 

• 5 i 

19.16 

I 43-3 

14-5 

5434 

2950 

840 

185 

.76 

.16 

1.6 

2.1 

1.36 

— 

58-9 

38-5 

— 

600 

989 

218 

1.61 

•35 

2-5 

•99 

1.06 

—• 

28.1 

3 °.i 

•—• 

395 

JI 55 

254 

.70 

•15 

•43 

2.27 

•38 

16.7 

64.4 

10.88 

4744 

2310 

1150 

253 

.72 

•15 

•43 

2.26 

•5 

16.4 

62.6 

14-5 

4654 

2300 

1617 

356 

.80 

•17 

.46 

1.98 

•34 

I 5-7 

56.2 

9.6 

447-5 

2156 

3427 

755 

25 

5 - 5 i 

•72 

.06 

5 - 1 

— 

1.8 

146.6 

— 

i 37 i 

116 

25 

2.50 

•55 

2.1 

.64 

.16 

2.99 

18.1 

4-5 

84.8 

464 

1767 

389 

— 


1.1 

— 

— 

7.6 

— 

— 

215.4 

883 

1861 

410 

.64 

.14 

.86 

2-5 

3-2 

.24 

7 1 - 1 

90.7 

6.8 

1163 

00 

\r 

M 

347 

.26 

.058 

•13 

6 

1.36 

58.8 

170 

38.5 

1667 

7890 

426 

94 

2.38 

•52 

1.1 

.67 

•35 

5-85 

19.05 

9-97 

166 

852 

632 

139 

1.24 

.27 

2.2 

1.29 

1.14 

— 

36 

32-4 

— 

45 i 

1411 

3 11 

3 -i 7 

.69 

1.4 

•5 

2.25 

•44 

14.28 

63-9 

12.7 

705 

198 

43 

1.11 

.24 

5 

1.44 

.11 

—• 

40.8 

3.26 

— 

198 

302 

66 

•44 

.098 

2-3 

3-58 

.04 

— 

101.7 

1.42 

— 

43 1 

741 

163 

1.09 

.24 

2 

1.47 

1.22 

— 

41.7 

34-7 

— 

494 

55 1 

121 

•79 

•17 

2.7 

2 

.42 

.16 

57-3 

12 

4-77 

3 6 7 

312 

68.9 

•93 

•205 

.96 

I - 7 I 

2 

2.67 

48.4 

574 

75 - 6 

1040 

169 

37-2 

• 3 ° 

.066 

•59 

5-3 

.48 

8.16 

149.7 

13.6 

231 

1690 

I 35 I 

298 

i -53 

•33 

1.4 

1.04 

2.1 

—- 

29.4 

59 - 6 

— 

676 

1740 

383 

.298 

.065 

•23 

5-36 

2.64 

26 

I 5 I -9 

74.8 

739-3 

435 ° 

220 

48 

5- I 7 

1.14 

13.6 

•3 

.06 

•17 

8.76 

1.81 

4.98 

73 

1710 

37 6 

.60 

• J 3 

•59 

2.62 

4.16 

2.64 

74-3 

H7.9 

74.8 

1710 

23 s ; 

51 

2.44 

•53 

2.9 

• 6 5 

.06 

2.09 

18.5 

1.78 

594 

336 

1208 

266 

•93 

.20 

•99 

1.72 

3.06 

— 

48.7 

86.7 

— 

1006 

i 59 8 

352 

1.47 

•32 

i - 2 5 

1.08 

2-55 

— 

30.8 

72-3 

— 

799 

292 

64 

1.10 

.24 

• 5 1 

i -45 

.08 

I 5 - 1 

41.1 

2.41 

428.1 

1947 

428 

94 

1.92 

•42 

.46 

•83 

•38 

16.72 

23-5 

10.88 

474 - 

2140 

1070 

235 

7-35 

1.62 

•93 

.21 

— 

8-97 

6.16 

— 

2.544 

1070 

1296 

285 

5-55 

1.20 

•77 

.28 

•43 

9.88 

8.16 

12.2 

280.3 

1296 

i 5 6 4 

344 

1.23 

•27 

• 5 i 

i -3 

.06 

15-38 

36.8 

i -7 

43 6 - 

1955 

154 

33 

9.21 

2.03 

4-54 

•17 

.1 

1.47 

4.92 

3-°7 

41.86 

220 

i860 

410 

— 

— 

•32 

— 

— 

26.66 

— 

— 

75 6 

3 100 

100 

22 

1.42 

• 3 1 

1 

1.12 

.64 

6.08 

3 1 -75 

18.14 

172.3 

1000 

5 ° 

11 

8-33 

1.83 

2 

.19 

.12 

3-84 

5-44 

3.62 

108.8 

500 
































352 


APPENDIX 


A man is too fleshy and wishes to reduce his weight. Suppose that he 
eats just enough to support his body without exercise. How far must he 
walk to take off five pounds of fat? 

An eight-year-old boy needs about half as much food as a man. What 
would be a fair amount of carbohydrate for a boy of this age? If an eight- 
year-old boy bought half a pound of candy and ate it all in one day, in 
addition to his usual food, how much carbohydrate would he get that day ? 

Suppose that in walking you use the same energy in proportion to your 
weight as does the average man. How much energy will you use in walk¬ 
ing a mile? 

How much energy would you use in climbing to the top of the tallest 
building that you know ? 

How much energy would be required to bring you from your home to 
your place in the schoolroom ? 

How much would it cost to buy enough bread to carry you ten miles ? 
enough filberts ? enough strawberries ? 

How much potatoes would a man need to eat to get ioo grams of proteid? 

How much beef would he need to eat to get 3000 Calories of energy ? 
How much proteid would this give him? 

A man had for breakfast two eggs (4 oz.), two slices of bacon (| oz.), 
3 slices of bread (4 oz.), butter (| oz.), and coffee with milk (1 oz.) and 
sugar Q oz.). How much proteid, fat, carbohydrate, and energy did he 
get? 

How much money would be required to buy in fresh fish the amount of 
proteid that can be bought for 10 cents in corn meal? the amount of 
energy that can be bought for 10 cents in oatmeal? 

If a man eats 100 grams of proteid and 100 grams of fat a day, how 
much carbohydrate will he need to give him 3500 Calories of heat ? 

If in the diet on page 349 the carbohydrates are decreased 100 grams, 
how much must the fats be increased to give the same amount of energy? 

Make up a diet of fish, bread, eggs, and cheese that will give a man 100 
grams of proteid. How much fat will this diet give him ? how much carbo¬ 
hydrates ? how much energv ? What would be the objection to this diet ? 

Select three foods from the list on page 350, and from them make a diet 
that will give a hard-working man the proper amounts of the different 
classes of foods and of energy. 

Weigh your own food for a day and calculate how much of the different 
classes of foods and how much energy you get. 


APPENDIX 


353 


B. INTESTINAL DISEASES 

The long intestinal tract affords a favorable place for the growth of 
parasites, and the parasites find an easy mode of entrance to this 
tract in the food and water that are taken in through the mouth. 
Children, especially, suffer from intestinal diseases, and because these 
diseases cause so much sickness and so many deaths, it is important 
that their cause and the means of prevention be understood. 

Diarrhoea. Diarrhoea may be caused by several different bacteria, 
all of which grow in the intestine, and most of which are closely 
related to the typhoid germ. One of these germs causes the very 
severe form of diarrhoea that runs in epidemics, and is sometimes 
called flux . Poisoning from meats, fish, old milk, and ice cream is 
due to germs related to the diarrhoea bacteria. The germs grow in 
the food either before or after it is eaten, and produce the toxins 
that cause the poisoning. 

Infant Diarrhoea. Summer complaint, from which so many young 
children die, is caused by germs belonging to this same group. The 
disease may easily be started in a little baby by giving it impure 
water, and nothing but boiled water, pure rain water, or artesian 
water should ever be given to a little child or put into its milk. 
Nearly all milk contains germs that, when taken in large enough 
numbers, will cause the trouble, and the milk supply is mainly respon¬ 
sible for the disease. The disease is worse in summer because in 
warm weather the germs multiply more rapidly in milk, and also 
because the heat weakens the children so that they have not much 
power of killing germs. 

How the Germs of Intestinal Diseases are Spread. The germs 
of diarrhoea, dysentery (page 296), and typhoid fever are usually 
swallowed either in food or water. They are carried about and 
get into the food and water in various ways (page 315), but one 
especially important precaution in the prevention of all these dis¬ 
eases is to keep discharges from the intestines away from flies. 


354 


APPENDIX 


Hookworms. The hookworm is a slender white worm, not quite 
half an inch in length. It grows in the intestines, and causes a pro¬ 
found anaemia (lack of red blood corpuscles). Hookworms are found 
in the warmer parts of all the continents; they cause the death of 
one third of the people of Porto Rico, and it is estimated that in 
our own country south of the Potomac River from 20 to 25 per 
cent of the poorer white people suffer from hookworms. 

How Hookworms get into the Body. The eggs of the hookworm 
pass out of the body in the excreta from the alimentary canal. If 
they are allowed to get into the soil, they develop into worms so small 
that there may be fifty of them in a piece of earth the size of a pea. 
These worms may enter the body through the skin (in which they 
cause “ground itch”) and be carried in the blood to the intestine, 
or they may be taken into the alimentary canal in water or in food. 
The disease is more common among children than among adults, 
because children go barefooted, and sometimes eat with unwashed 
hands after playing in the earth; it is more common among agricul¬ 
tural laborers and brickmakers than among those who do not come 
in contact with the soil; and the disease is more severe (though not 
more common) in the white than in the colored race. 

The Prevention of Hookworm Disease. The eggs of the hookworm 
get into the soil only from persons who have the disease. Away 
from the air the eggs die, and the disease may be entirely prevented 
by the use of closets. In hookworm regions great care, there¬ 
fore, should be exercised to prevent the pollution of the soil about 
houses. To a certain extent, children may be saved from infection 
by the wearing of shoes, but keeping the soil free from pollution 
is the important measure in the prevention of hookworm disease. 1 


1 Often it is not realized that hookworm victims are diseased, and they are 
considered lazy and ambitionless. Many cases of hookworm trouble are 
mistaken for malaria. The symptoms of hookworm disease are paleness, thin¬ 
ness, dull skin and eyes, dry hair, continued weakness, and sometimes an appetite 
for such substances as earth, tobacco ashes, and paper. The worms may 
readily be killed and the disease cured by the use of very simple medicines. 


GLOSSARY 


This glossary is intended chiefly to help the pupil in the pronunciation of the more 
difficult terms. Words are defined only where no exact definition is found in the text. 
The numbers refer to the pages on which definitions are found. 


afferent (af fe-rent), carrying to. 
amoeba (am-e'ba), 296. 
amylopsin (a-ml-lop'sin), 98. 
Anopheles (an-ofel-ez), 321. 
aorta (a-or'ta), 141. 
aqueous (a'kwe-us), watery. 
arachnoid (a-rak'noid), like a cob¬ 
web ; as, arachnoid membrane. 
arbor vitae (ar'bor vi'te), 215. 
arytenoid (a-rf-te'noid), 173. 
bacillus (ba-sfl'lus), 304. 
bacteria (bak-te're-a), 285. 
biceps (bi'seps), 67. 
bronchial (bron'ke-al), 166. 
canine (ka-nin'), 95. 
capillary (cap'il-la-re), 141. 
carbohydrate (kar-bo-hl'drat), 82. 
cartilage (kar'til-aj), gristle. 
cerebellum (ser-e-bel'lum), 25. 
cerebro-spinal (ser'e-bro-spi'nal), 26. 
cerebrum (ser'e-brum), 25. 
choroid (ko'roid), 261. 
cilia (sil'e-a), plural of cilium; 

minute , hair-like projections. 
coccus (kbk'us), 304. 
coccyx (kok'six), 34. 
cochlea (kok'le-a), 254. 
corpuscle (kor'pusl), a cell of the 
blood or lymph (page 147), or a 

355 


group of cells, as a renal corpuscle 
(page 188). 
cricoid (kri'koid), 172. 

Culex (kyu'lex), 321. 
cytoplasm (sl'to-plazm), 4, footnote, 
dentine (den'tln), 94. 
diaphragm (di'a-fram), 17. 
dietetics (di-e-tet'iks), the science or 
study of the regulation of the diet. 
diphtheria (dif-the're-a), 304. 
dura mater (du'ra ma'ter), 26. 
efferent (effe-rent), carryingfrom. 
enzyme (en'zlm), 112. 
epiglottis (ep-T-glot'tis), 165. 
esophagus (e-sof'a-gus), 90. 
Eustachian (yu-stak'e-an), 253. 
fasciculus (fas-sTk'yu-lus), a bundle. 
femur (fe'mer), 37. 
fibula (fib'yu-la), 37. 
formaldehyde (for-mal'de-hid), 335. 
fungus (fun'gus), plural fungi (fun r - 

j0> 318. 

hemoglobin (hem-6-glo'bin), 148. 
hepatic (he-pat'ik), pertaining to the 
liver; as, hepatic vein. 
hydrogen (hi'dro-jen), 80. 
incisor (in-si'sor), 95. 
infundibulum (in-fun-dtb'yu-lum), 
166. 



356 


GLOSSARY 


invertase (in-ver'tas), 113, footnote, 
lachrymal (lak'ri-mal), pertaining to 
the tears; as, lachrymal duct. 
lacteal (lak'te-al), 152. 
larynx (lar'inks), 165. 
lymph (llmf), 149. 
lymphatic (lim-fat'ik). 
malleus (mal'le-us), 253. 
medulla oblongata (med-ul'la ob- 
lon-gah'ta), 25. 

Meibomian (mi-bo'mi-an), 260. 
membrane (mem'bran), a thin layer 
of tissue. 

meningitis (men-in-jl'tis), 308. 
molecule (mol'e-kyul), 79. 
mucus (myu'kus), 168. 
neuron (new'ron), 211. 
nitrogen (nl'tro-jen), 80. 
nucleus (new'kle-us), 4. 
olfactory (ol-fak'to-re), pertaining to 
the sense of smell. 
pancreas (pan'kre-as), 98. 
papilla (pa-pil'la), 193. 
parotid (pa-rot'id), 97. 
patella (pa-tel'la), 37. 
peptone (pep'ton), 112. 
perimysium (per-e-mlz'e-um), 62. 
periosteum (per-e-os'te-um), 42. 
phalanges (fa-lan'jez), 37. 
pharynx (far'inks), 90. 
pia mater (pl'a ma/ter), 26. 
process (pro'sess), a slender , pro¬ 
jecting point. 
proteids (prd'te-ids), 83. 
protoplasm (pro'to-plazm), the living 
substance of the cell. 
protozoon (prd-to-zo'on), plural pro¬ 
tozoa (pro-to-zd'a), 285. 


psoas (so'as), 70. 
ptyalin (tl'a-lin), 98. 
pulmonary (pubmo-na-re), having to 
do with the lungs. 
pylorus (pi- 16 'rus), 93. 
rabies (ra'be-ez), 299. 
renal (re'nal), pertaining to the kid¬ 
neys', as, renal corpuscle. 
retina (ret'i-na), 261. 
sacrum (sa'krum), 34. 
salivary (sal'i-va-re), 89. 
scapula (skap'yu-la), 36. 
sclerotic (skle-rot'ik), 261. 
sebaceous (se-ba'shus), 195. 
spirillum (spl-ririum), 304. 
stapes (sta'pez), 253. 
steapsin (ste-ap'sin), 98. 
subcutaneous (sub-kyu-ta'ne-us), 193. 
submaxillary (sub-maks'il-la-re), 97. 
tetanus (tet'a-nus), 313. 
thoracic (tho-ras'ik), connected with 
the chest , from thorax, chest. 
thyroid (thl'roid), 172. 
trachea (tra'ke-a), the windpipe. 
trapezius (trap-e'ze-us), 60. 
triceps (tri'seps), 67. 
trichina (trT-kl'na), 129. 
trichinosis (trik-T-no'sis), 129. 
trypsin (trTp'sin), 98. 
tuberculosis (tu-ber-kyu-lo'sis), 340. 
tympanic (tTm-pan'ik), 252. 
tympanum (tim'pan-um), 253. 
urea (yu're-a), 116. 
ureter (yu-re'ter), 188. 
uvula (yu'vyu-la), 165. 
vena cava (ve'na ka'va), plural 
venae cavae (ve'ne ka/ve), 142. 
vitreous (vlt're-us), like glass. 



INDEX 


A star (*) after a page number indicates that an illustration of the subject ap¬ 
pears on that page. 


Abdominal cavity, 16,* 17; muscles, 
60,* 70 .* 

Absorption, 93, 110-119. 

Accidents, 274-283. 

Acid, in gastric juices, 91,* 92, 113, 
113; uric, 114, 116; poison, 280. 

Afferent nerves, 211, 217, 218,* 225,* 
226,* 245, 246,* 248. 

Air, 80, 178, 180, 229, 344. See also 
Oxygen and Carbon Dioxid. 

Air sacs, 161, 162,* 166, 167.* 

Alcohol as a food, 131; baths, 199 
(n. 1); how formed, 238; and 
length of life, 239; and tuberculosis, 
240; and insanity, 241; and germ 
diseases, 290. 

Alcohol, effects of, on the human body, 
238-244; muscles, 74, 233; diges¬ 
tive organs, 101, 102, 116; heart, 155; 
arteries, 155; respiratory system, 
171; kidneys, 189; nervous system, 
232*; animals, 233, 234,* 241; char¬ 
acter, 243; eyes, 271. 

Alimentary canal, 88; disease germs 
in, 287, 315, 353. 

Amylopsin, 98, 113. 

Anatomy, defined, 13. 

Animal kingdom, 17, 19.* 

Animals, composed of cells, 4, 5, 11; 
one-celled, 5, 6,* 7, 150. 

Antitoxins, 287 (n. 2), 306, 307. 

Aorta, 138,* 141, 143,* 186 .* 

Appendix, vermiform, 88,* 94, 94 (n. 2). 

Aqueous humor, 261.* 

Arachnoid membrane, 26. 

Arbor vitae (“tree of life”), 213,* 215. 


Arteries, pulmonary, 138,* 141, 143*; 
hepatic, 138*; aorta, 138,* 141; 
defined, 141; circulation in, 140, 
142*; bleeding from, 277,* 278.* 

Arytenoid cartilages, 172,* 173, 174.* 

Atoms, 79-81. 

Auditory canal. See Hearing. 

Auricles, 137,* 140, 141, 143 * 

Bacilli, 304.* See also Bacteria. 

Bacteria, diseases caused by, 303-318; 
in foods, 130, 315, 327, 330, 353; 
defined, 285; shapes of, 304*; of 
various diseases, 305,* 308,* 310,* 
311,* 313,* 315,* 316* 317,* 340* 

Baths, 200-203. 

Bile, duct, 90*; in the liver, 99. 

Bladder, gall, 88,* 90,* 99; of kidneys, 
186,* 189. 

Bleeding, 277,* 278.* 

Blood, cells of, 7, 10,* 147* (see also 
Corpuscles ); circulation of, 135—157; 
function of, 135. 

Blood vessels, 17, 26, 27,* 42, 91,* 
93,* 136, 138,* 141, 143,* 143, 

146,* 161, 162,* 191,* 195,* 198. 

Body, human, a colony of cells, 3-15, 
135; plan of, 16-22; cavities of, 16,* 
17; controlled by nervous system, 
28, 210; carriage of, 53, 69-72; laws 
governing, 135; wastes of, see Wastes ; 
heat of, 135, 191, 194, 197-199, 
202; effects of alcohol on, 238-244; 
equilibrium of, 255. 

Bone, cells of, 7, 8,* 56; materials in, 
39, 40*; marrow, 40,* 42, 147. 


357 , 



358 


INDEX 


Bones, of the skeleton, 31-43, 32,* 
33,* 34,* 35,* 5°*, 5 2 *5 broken, 55. 
Brain, 8,* 17,* 23, 24,* 25,* 48, 210, 
210 (n. 1), 213,* 265. 

Bright’s Disease, alcohol and, 189. 
Bronchial tubes, 166, 167.* 

Burns, treatment of, 279. 

Calorie, 348, 348 (n. 1). 

Capillaries, 138,* 141, 142,* 144 (n. 1), 
148,* 150,* 151 * 

Carbohydrates, 82, 83, 124-128, 349. 
Carbon dioxid, 81,* 148, 150,* 160, 
179, 180 (n. 1). 

Cartilage, 35,* 38* 42,* 47* 50; 
thyroid, 172*; cricoid, 172*; aryte¬ 
noid, 87,* 172,* 173, 174.* 

Cat, brain of, 229*; eyes of, 262.* 

Cell, the, 3-15; division of, 5,* 6.* 
Cells, human body a colony of, 3-15; 
kinds of, 7,* 8,* 10, 89,* 56, 59 
(n. 1), 61, 91* 188, 191,* 193, 200; 
ciliated, 9,* 147 (n. 1); growth of, 78, 
84; energy in, 78, 84, 114; wastes of, 
US>* x 49 » 15 °*; foods of, 7, 78, 79, 
114, 115,* 150*; poison in, 186, 287. 
Cerebellum, 25,* 213,* 215, 229.* 
Cerebro-spinal fluid, 26; meningitis, 26 
(n. 1), 317 * 

Cerebrum, 25,* 213,* 214,* 229.* 
Chemistry of foods, 79, 80,* 81,* 82. 
Chest (thoracic) cavity, 16,* 17, 162.* 
Chills, 199, 202, 203, 293. 

Cholera, 316.* 

Choroid coat of the eye, 261,* 262, 266. 
Cigarettes. See Tobacco. 

Cilia, 6,* 9,* 147 (n. 1), 168. 

Ciliary muscles, 266.* 

Circulation of the blood, 135-159; 
diagram of, 138*; organs of, 136- 
146, 139,* 142,* 143,* 146.* 

Clavicle (collar bone), 32,* 35,* 36. 
Cleanliness, 130, 200-202. 

Climate and tuberculosis, 346. 


Clothing, 170, 204, 205, 279. 

Cocci {sing, coccus), 304.* 

Coccyx, 34.* 

Cochlea, 254.* 

Colds, 203, 310. 

Compounds, 79-81. 

Connective tissue, 8,* 11, 25, 27,* 42, 
47,* 62,* 63,* 89,* 91,* 143, 191.* 
Consumption. See Tuberculosis. 
Contraction, of muscles, 61, 65, 66*; of 
auricles and ventricles, 137, 140; 
governed by the cerebellum, 215. 
Convolutions of the brain, 25,* 214. 
Cooking, 123, 128. 

Cornea, 261,* 266.* 

Corpuscles, red, 7, 10,* 42, 85, 147,* 
148, 293*; white, 10,* 147,* 153, 
288*; renal, 187,* 188*; touch (tac¬ 
tile), 191,* 246,* 247. 

Cranial nerves, 225. 

Cranium, 25, 26,* 34, 48. 

Cricoid cartilage, 172.* 

Cytoplasm, 4 (n. 2). 

Dermis, 191,* 193, 195.* 

Diaphragm, 16,* 17,* 18,* 162 (n. 1), 
163,* 164 (n. 1). 

Diarrhoea, 353. 

Dietetics, 120-133. 

Digestion, 7, 9, 110-119, 121-123; 

organs of, 88-109, 88 ,* 9°*5 alco¬ 
hol and, 101, 116; juices in, 91, 93, 
100; hygiene of, 120-123. 
Diphtheria, 304-307, 305*. 

Disease germs, 285-290; and lymph 
nodes, 153, 154; defined, 285; alco¬ 
hol and, 290; in water, 315,* 324, 
327-329; in milk, 316 (n. 1), 330. 
See also Bacteria, Protozoa, etc. 
Diseases, intestinal, 353-354. 
Disinfection, 312, 332-338. 

Dorsal cavity, 16.* 

Drowning accidents, 274,* 275,* 276.* 
Ducts. See Salivary, Thoracic, etc. 



INDEX 


359 


Dura mater, 26. 

Dust, 170, 271, 325-327. 

Dysentery, 296.* 

Ear, bones of, 34, 253*; divisions of, 
25 2 >* 253, 254*; care of, 255. 

Ear drum (tympanum), 253. 

Efferent nerves, 211, 218,* 219,* 226.* 
Elements, 79-81. 

Energy, foods and, 78-87, 114, 124, 
349; in the cells, 78, 84, 114; oxida¬ 
tion and, 114, 160, 348. 

Enzymes (ferments), 112, 113. 
Epidermis, 191,* 192,* 195.* 

Epiglottis, 165, 166,* 173.* 

Epithelium, 249, 249 (n. 1). 

Erector spinae, 70,* 71.* 

Erysipelas, 311.* 

Esophagus, 17,* 88,* 90, 166.* 
Eustachian tube, 252,* 253. 

Exercise, 12, 73, 123, 154, 170. 

Eyes, 259-273; and digestion, 123; 
effects of tobacco on, 271-272; 
foreign bodies in, 278. 

Fainting, 278. 

Fat, 8,* 10, 42, 115, 191 .* 

Fats, as food, 83, 113, 124, 153. 
Ferments (enzymes), 112, 113. 

Fever, 198, 293. 

Fibers. See Nerve, Muscle, etc. 

Flies, dangers from, 324,* 325.* 
Follicle, hair, 194, 195,* 200 (n. 1). 
Foods, for the cell, 7, 78, 79, 114, 
II5 * IS o*; and energy, 78-87, 
114, 124, 349; chemistry of, 79-82; 
classes of, 82-84; digestion of, 
110-119, 121-123; oxidation of, 

114, 160, 348; amount and kinds 
needed, 124-128, 348; alcohol and, 
131-132; for consumptives, 344; 
table of, 350-351. 

Foot, 48,* 49, 146.* 

Fungi, 287 (n. 1), 318.* 


Gall bladder, 88,* 90. 

Ganglia, 210, 226, 227,* 228.* 

Gastric glands and juice, 91,* 92. 

Germicidal substance, 288, 290. 

Germs. See Disease Germs, Bacteria. 

Glands, stomach, 7,* 25, 25 (n. 1), 91*; 
salivary, 25 (n. 1), 89, 97,* 98*; 
pancreas, 25 (n. 1), 98; liver, 25 
(n. 1), 99; kidney, 25 (n. 1); sweat, 
25 (n. 1), 89 (n. 1), 191 ,* 193* 194; 
simple, 89*; secretions of, 89, 
89 (n. 1); cells of, 7,* 89,* 91*; gas¬ 
tric, 91*; intestinal, 93*; sublingual, 
97*; submaxillary, 97*; parotid, 
97*; sebaceous, 195; lachrymal, 
259, 260*; Meibomian, 260. 

Grape sugar, 112, 113. 

Gray matter (nerve cells), 214, 217, 
229. 

Hair, 194, 195,* 196. 

Hand, n, 37, 64,* 65 * 

Health officials, importance of, 338. 

Hearing, 251-256; organ of, 252,* 
253 ,* 254 * 

Heart, location of, 17,* 18,* 137, 139*; 
function of, 137; auricles, 137*; 
ventricles, 137*; valves of, 140,* 
141*; nerves of, 145; hygiene of, 
154-156; alcohol and, 155; tobacco 
and, 156; and the great blood 
vessels, 141, 142, 143.* 

Heat. See Body Heat, Heating. 

Heating and ventilation, 182, 197, 
202. 

Hemispheres of the cerebrum, 214. 

Hemoglobin, 148. 

Hepatic, vein and artery, 138,* 145. 

Heredity, and alcohol, 241; and tuber¬ 
culosis, 240, 345, 345 (n. 1). 

Hookworms, 354. 

Hydrophobia. See Rabies. 

Hygiene, defined, 13; of the skeleton, 
53-56; muscles, 73-74; digestive 



360 


INDEX 


organs, 120-123; heart, 154-156; 
respiratory system, 170-172; nervous 
system, 229-235. 

Impulses, nerve, 211, 216, 217, 245. 
Incus (anvil), 253.* 

Influenza (Grip), 309, 310.* 

Insects, as disease carriers, 287, 320- 
3 2 5 > 321,* 322,* 324,* 325-* 
Intestinal diseases, 315,* 316,* 353. 
Intestine, 17,* 18*; large, 88,* 94; 

small, 88,* 93,* 113, 152. 
Involuntary muscles, 25, 61 (n. 1), 62. 
Iris, 261,* 262,* 266.* 

Iron, 80*; in the blood, 85. 

Joints, 45, 46, 48*; muscles and, 61. 
Juices, digestive, 91-93, 98, 100, 112. 

Kidneys, 7, 17* 25 (n. 1), 186,* 187*; 
and the body wastes, 186-190; 
alcohol and, 189. 

Knee-cap. See Patella. 

Lachrymal, bone, 33*; glands, 259, 

1 260.* 

Lacteals, 151,* 152 (n. 1). 

Larynx, .165, 166,* 167,* 172*, 173.* 
Lens, of the eye, 261,* 263, 264,* 266.* 
Ligaments, 47, 48,* 55; and tendons, 
64,* 65*; suspensory, 263, 266.* 
Light, and the sense of sight, 262-267, 
270; and disease germs, 333. 

Liver, 11, ,17,* 18,* 25 (n. 1), 88,* 89; 
and alcohol, 102, 116; circulation 
in, 138,* 145 (n. t). 

Lumbar region, 69. 

Lungs, 7, 9, 11, 17* 18,* 148 (n. 1), 
161, 163,* 167*; circulation in, 138,* 
162*; air sacs in, 161, 162,* 166, 
167*; in drowning accidents, 274. 
Lymph, 149, 150,* 151 (n. 1), 194; 
nodes, 139,* 152,* 153*; and disease 
germs, 154, 154 (n. 1). 


Lymphatic, system, 151-154; vessels, 
139,* 151,* 152 (n. 1). 

Malaria, 292-296; germ of, 293,* 
295 (n. 1); mosquitoes and, 294- 
296, 321,* 322,* 323. 

Malleus (hammer), 253.* 

Malt sugar, 111, 113. 

Mammals, 18, 19.* 

Man, in animal kingdom, 17, 18, 19.* 

Medicines, patent, 12, 130, 343. 

Medulla, 25,* 213,* 216, 229.* 

Meibomian glands, 260. 

Membranes, of brain and cord, 25, 
26; mucous, 90, 91,* 151,* 168.^ 

Meninges, 26 (n. 1); disease of, 317. 

Milk, germs in, 33°“332, 34 1. 

Mind, the seat of, 25, 210 (n. 1), 214. 

Mineral matter, in bone, 39; foods, 85. 

Molecules, 79, 80,* 81,* no, in, 114. 

Mosquitoes and malaria, 294-296, 
321,* 322,* 323. 

Motor nerves. See Efferent. 

Mucous membrane, 90, 91,* 151,* 168. 

Mucus, 9,* 90, 94, 168. 

Muscle, cells, 7, 8,* 10, 61 (n. 1), 62,* 
150,* 211*; tissue, 10, 59 (n. 1); 
fibers, 143. 

Muscles, the, 59-77, 60*; voluntary, 
23-25, 61 (n. 1), 68, 215; involun¬ 
tary, 25, 61 (n. 1), 62; contraction of, 
61, 65, 66,* 215; antagonistic, 67; 
of head, 69*; of spinal column, 
69, 70,* 71,* 72; effects of alcohol 
and tobacco on, 74; of stomach, 92; 
of the hair, 195,* 195 (n. 1); of the 
eye, 260*; ciliary, 266.* 

Nails, the, 196. 

Nasal, bone, 33*; passages, 164, 166,* 
168; cavity, 260.* 

Nerves, cells (gray matter), 8,* 210; 
tissue, 10, 210; of brain, 10, 26, 
219 (n. 1), 214, 229; fibers, 27,* 192,* 




INDEX 


210, 2ii,* 219*; function of, 27; in 
bone, 42; of the heart, 145; of the 
skin, 191,* 192*; cranial, 225; 

of touch, 246,* 247; of taste, 249*; 
optic, 260,* 261,* 265. See also 
Afferent and Efferent. 

Nervous system, 23-30, 210-237; 

central, 23, 213-224; sympathetic, 
23, 226-228; like a telegraph sys¬ 
tem, 28; and the muscles, 68; and 
the sweat glands, 194; like a tele¬ 
phone system, 212*; of other ani¬ 
mals, 229*; hygiene of, 229-235; 
tobacco and alcohol and, 230-235. 

Neurons, 211,* 218. 

Nitrogen, 80, 84. 

Nodes. See Lymph. 

Nucleus, of cells, 4, 61 (n. 1), 211*; 
division of, 5,* 6.* 

Olfactory organs. See Smell. 

Optic nerve, 260,* 261,* 265. 

Organs of the body, n, 17,* 18,* 23. 

Oxidation of foods, 114-115, 160,* 348. 

Oxygen, and the cells, 7, 9, 114, 148, 
148 (n. 1), 161; carried by red cor¬ 
puscles, 7, 148, 148 (n. 1); in air, 
178, 179. See also Oxidation. 

Pancreas, 17,* 25 (n. i), 88,* 89, 90,* 
98, 113; juices of, 98, 113. 

Papillae, 191,* 192,* 193, 195 * 

Pasteur treatment, 300. 

Patella (knee-cap), 32,* 37, 60.* 

Pelvis, bones of, 32,* 35,* 36. 

Pepsin, 89 (n. 1), 92. 

Peptones, 112. 

Pericardium, 163,* 163 (n. 1). 

Periosteum, 40,* 42,* 63, 64. 

Pharynx (throat), 90, 164, 166.* 

Physiology, defined, 13. 

Pia mater, 26. 

Plasma, 146, 147, 149. 

Pleura, 161, 162,* 163.* 


361 

Pneumonia, 308, 309; germ of, 

308* 

Poisoning, treatment for, 280-281. 
Poisons, in cells, 120, 121 (n. 1), 186, 
287; in air, 178, 179. 

Pons, 213,* 216. 

Portal circulation, 138,* 145 (n. 1). 
Processes, bone, 38*; spinous, 38*; 
vocal, 172.* 

Proteids, 83, 113, 124, 125, 153, 348. 
Protoplasm, 4, n, 12, 13, 61 (n. 1), 
78, 84. 

Protozoa, 285, 292-302. 

Ptyalin, 98, 112. 

Pulmonary, artery, 138,* 141, 143*; 

veins, 138,* 142. 

Pupil of the eye, 261,* 262.* 

Pylorus, 90,* 93, 113. 

Quarantine, 306. 

Quinine, 256, 295, 296. 

Rabies (Hydrophobia), 299-300. 
Reflex, centers, 217, 219; actions, 
217, 218,* 219,* 220, 221, 227. 
Renal, artery, 186*; vein, 186*; cor¬ 
puscles, 187,* 188.* 

Respiration, 160-177; organs of, 161, 
162,* 163,* 164, 165, 166,* 167, 168; 
artificial, 274,* 275,* 276.* 

Rest, 12, 73, 271, 344 - 
Retina, 261,* 265,* 267,* 269. 

Ribs, 32,* 35,* 36. 

Sacrum, 34,* 35 * 

Salivary glands, 25 (n. 1), 89, 97,* 98.* 
Scapula, 32* 35,* 36, 38 * 

Sclerotic coat of the eye, 261,* 266. 
Sebaceous glands, 195.* 

Semicircular canals, 254,* 255. 
Sensations, 215, 245. 

Senses, the special, 245-273. 

Sensory nerves. See Afferent Nerves. 
Shoulder blade. See Scapula. 



362 


INDEX 


Skeleton, the, 31-58, 32*; principal 
bones of,. 33,* 34,* 35>* 3 6 > 37 i 
effect of tobacco on, 56. 

Skin, the, 8,* 191,* 192,* 195, 246*; 

and the body heat, 191-208. 

Skull, 32* 33.* 

Sleep, 183-184, 229-230. 

Smallpox, 297,* 298. 

Smell, the sense of, 250,* 251. 

Spinal column, 16,* 17, 31, 32,* 34,* 
49 > 54 , 69, 71. 

Spinal cord, 16, 17,* 24,* 25, 26,* 28, 
217, 219, 225,* 226,* 227,* 228.* 
Spinous processes, 38,* 70. 

Spirilla, 304.* 

Spleen, 17,* 18,* 88,* 138* 

Sputum, 305, 308, 326, 342. 

Stapes (stirrup), 253.* 

Starch, 82, hi, 113, 116. 

Steapsin, 98, 113. 

Sternum (breast bone), 32,* 35.* 
Stimuli, nerve (impulses), 211, 216. 
Stomach, 7,* 9, 17,* 18,* 88,* 90,* 

91,* 92,* 138*; function of, 91; of 
various animals, 105.* 

Subcutaneous layer, 191,* 193. 

Sugar, a carbohydrate, 82; digestion 
of, in, 113, 145 (n. 1); malt, in, 
11 35 g ra P e , 112, 113; and villi, 153. 
Suspensory ligament, 263, 266.* 

Sweat glands, 25 (n. 1), 89 (n. 1), 191,* 
193,* 194, 198, 227. 

Sympathetic nervous system, 23, 62, 
226-228, 227.* 

Tactile (touch) corpuscles, 246,* 247. 
Tapeworm, 129,* 129 (n. 1). 

Taste, 246, 249.* 

Teeth, 89, 94, 95,* 96* 103. 
Temperature. See Body Heat, Heating. 
Tendons, 63,* 64.* 

Tetanus (lockjaw), 313,* 314. 

Thoracic (chest) cavity, 16,* 17, 162*; 
duct, 152, 153. 


Thyroid cartilage, 172.* 

Tissues, 10, 59 (n. 1), 210. 

Tobacco, effects of, on the skeleton, 
56; muscles, 74; heart, 156-157; 
respiratory system, 172; nervous 
system, 230-232; eyes, 271-272. 
Tongue, 97,* 104.* 

Tonsils, 165. 

Touch, 191,* 246,* 247,* 248.* 
Toxins, 287, 293. 

Trachea, 9,* 17,* 161, 163,* 165, 166.* 
Trichina, 129.* 

Trypsin, 98, 113. 

Tuberculosis, 240, 34o*-346. 
Tympanic membrane, 252,* 253.* 
Tympanum (ear drum), 253. 

Typhoid fever, 286, 315,* 316 (n. 1), 
324, 327, 328. 

Urea, 116, 186, 187; alcohol and, 116. 
Ureter, 186,* 187,* 188. 

Uric acid, 114, 116, 186, 187. 

Uvula (soft palate), 165, 166.* 

Vaccination, 297-299. 

Valves of the heart, 137,* 140,* 141.* 
Veins, 89,* 138,* 141, 142,* 143,* 
186*; bleeding from, 277. 

Venae cavae, 137,* 138,* 142,* 143.* 
Ventilation, 178-185, 182,* 183.* 
Ventral cavity, 16,* 17. 

Ventricles, 137,* 140, 143.* 

Vertebrae, 34,* 38.* 

Vertebrates, 18, 19,* 20, 5o*~53. 

Villi, 93,* 94 (n. 1), 151,* 152. 

Vitreous humor, 261.* 

Vocal cords, 165, 172* 173,* 174,* 175. 
Voluntary muscles, 23, 61, 62, 215. 

Wastes, 7, 17, 114, 115,* 136, 149, 150 * 
Water, 81,* 187, 191, 191 (n. 1); and 
disease germs, 286, 315, 327-330, 

Yeast, 238.* 






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